Oxygen-scavenging compositions and articles

ABSTRACT

Oxygen-scavenging compositions comprising an oxidizable metal component, an electrolyte component and a solid, non-electrolytic, acidifying component. When blended with soft, flexible polymeric resins, these compositions exhibit good oxygen-scavenging performance with improved oxidation efficiency relative to compositions containing an oxidizable metal component, an electrolyte, and an acidifying component combined with a more rigid thermoplastic resins. Selection of a thermally stable non-electrolytic, acidifying component is important when melt compounding the compositions into polymeric resins and particularly for extrusion coating applications. The compositions can be used directly as an oxygen absorbent resin melt-fabricated into a wide variety of oxygen-scavenging packaging articles or as concentrates in combination with other thermoplastic resins.

[0001] This is a continuation-in-part of copending application Ser. No.08/483,302 filed Jun. 7, 1995, which is a continuation-in-part ofapplication Ser. No. 08/249,758 filed May 25, 1994, now abandoned, whichis a divisional of application Ser. No. 08/092,722 filed Jul. 16, 1993,now abandoned.

FIELD OF THE INVENTION

[0002] This invention relates to oxygen-scavenging compositions havingutility in packaging and other applications.

BACKGROUND OF THE INVENTION

[0003] Products sensitive to oxygen, particularly foods, beverages andmedicines, deteriorate or spoil in the presence of oxygen. One approachto reducing these difficulties is to package such products withpackaging materials containing at least one layer of a so-called“passive” gas barrier film that can act as a physical barrier totransmission of oxygen but does not react with oxygen. Films obtainedfrom ethylene vinyl alcohol copolymer (EVOH) or polyvinylidenedichloride (PVDC) are commonly used for this purpose due to theirexcellent oxygen barrier properties. By physically blocking transmissionof oxygen, these barrier films can maintain or substantially maintaininitial oxygen levels within a package. Because passive barrier filmscan add cost to a packaging construction and do not reduce levels ofoxygen already present in the packaging construction, however, there isa need for effective, lower cost alternatives and improvements.

[0004] An approach to achieving or maintaining a low oxygen environmentinside a package is to use a packet containing an oxygen absorbentmaterial. The packet, also sometimes referred to as a pouch or sachet,is placed in the interior of the package along with the product.Sakamoto et al. discloses oxygen absorbent packets in Japan Laid OpenPatent Application No. 121634/81 (1981). A typical ingredient used inthe oxygen scavenger carried in the packet is reduced iron powder whichcan react with oxygen to form ferrous oxide or ferric oxide, asdisclosed in U.S. Pat. No. 4,856,650. Also, it is known to include inthe packet, along with iron, a reaction promoter such as sodiumchloride, and a water-absorbing agent, such as silica gel, as describedin U.S. Pat. No. 4,992,410. Japan Laid Open Patent Application No.82-24634 (1982) discloses an oxygen absorber composition comprising 100parts by weight (pbw) iron powder, 2 to 7 pbw ammonium chloride, 8 to 15pbw aqueous acid solution and 20 to 50 pbw of a slightly water solublefiller such as activated clay. Japan Laid Open Patent Application No.79-158386 (1979) discloses an oxygen arresting composition comprising ametal, such as iron, copper or zinc, and optionally, a metal halide suchas sodium chloride or zinc chloride at a level of 0.001 to 100 pbw to 1pbw of metal and a filler such as clay at a level of 0.01 to 100 pbw to1 pbw of metal.

[0005] Although oxygen absorbent or scavenger materials used in packetscan react chemically with oxygen in the package, also sometimes referredto as “headspace oxygen”, they do not prevent external oxygen frompenetrating into the package. Therefore, it is common for packaging inwhich such packets are used to include additional protection such aswrappings of passive barrier films of the type described above. Thisadds to product costs. With many easy-to-prepare foods, anotherdifficulty with oxygen scavenger packets is that consumers maymistakenly open them and consume their contents together with the food.Moreover, the extra manufacturing step of placing a packet into acontainer can add to the cost of the product and slow production.Further, oxygen absorbent packets are not useful with liquid products.

[0006] In view of these disadvantages and limitations, it has beenproposed to incorporate directly into the walls of a packaging article aso-called “active” oxygen absorber, i.e., one that reacts with oxygen.Because such a packaging article is formulated to include a materialthat reacts with oxygen permeating its walls, the packaging is said toprovide an “active-barrier” as distinguished from passive barrier filmswhich block transmission of oxygen but do not react with it.Active-barrier packaging is an attractive way to protectoxygen-sensitive products because it not only can prevent oxygen fromreaching the product from the outside but also can absorb oxygen presentwithin a container.

[0007] One approach for obtaining active-barrier packaging is toincorporate a mixture of an oxidizable metal (e.g., iron) and anelectrolyte (e.g., sodium chloride) into a suitable resin, melt processthe result into monolayer or multilayer sheets or films and form theresulting oxygen scavenger-containing sheets or films into rigid orflexible containers or other packaging articles or components. This typeof active-barrier is disclosed in Japan Laid Open Patent Application No.56-60642 (1981), directed to an oxygen-scavenging sheet composed of athermoplastic resin containing iron, zinc or copper and a metal halide.Disclosed resins include polyethylene and polyethylene terephthalate.Sodium chloride is the preferred metal halide. Component proportions aresuch that 1 to 500 parts metal halide are present per 100 parts resinand 1 to 200 parts metal halide are present per 100 parts metal.Similarly, U.S. Pat. No. 5,153,038 discloses plastic multilayer vesselsof various layer structures formed from a resin composition formed byincorporating an oxygen scavenger, and optionally a water absorbingagent, in a gas barrier resin. The oxygen scavenger can be a metalpowder such as iron, low valence metal oxides or reducing metalcompounds. The oxygen scavenger can be used in combination with anassistant compound such as a hydroxide, carbonate, sulfite, thiosulfite,tertiary phosphate, secondary phosphate, organic acid salt or halide ofan alkali metal or alkaline earth metal. The water absorbing agent canbe an inorganic salt such as sodium chloride, calcium chloride, zincchloride, ammonium chloride, ammonium sulfate, sodium sulfate, magnesiumsulfate, disodium hydrogenphosphate, sodium dihydrogenphosphate,potassium carbonate or sodium nitrate. The oxygen scavenger can bepresent at 1 to 1000 weight % based on weight of the barrier resin. Thewater absorbing agent can be present at 1 to 300 weight % based onweight of the barrier resin.

[0008] One difficulty with scavenger systems incorporating an oxidizablemetal (e.g., iron) and a metal halide (e.g., sodium chloride) into athermoplastic layer is the inefficiency of the oxidation reaction. Toobtain sufficient oxygen absorption in active-barrier packaging, highloadings of scavenger composition are often used. This typicallyrequires that sheets, films and other packaging layer or wall structurescontaining a scavenging composition be relatively thick. This, in turn,contributes to cost of the packaging material and may precludeattainment of thin packaging films having adequate oxygen-scavengingcapabilities.

[0009] Another oxygen-scavenging composition, disclosed in U.S. Pat. No.4,104,192, comprises a dithionite and at least one compound having waterof crystallization or water of hydration. Listed among these compoundsare various hydrated sodium salts, including carbonate, sulfate, sulfiteand phosphates; sodium pyrophosphate decahydrate is specificallymentioned. As disclosed in Table 1, Example 1 of the patent, sodiumpyrophosphate decahydrate was the least effective of the compoundstested. In addition, use of hydrate containing compounds may notsuitable in oxygen-scavenging resins that require high temperatureprocessing. Thus, while a variety of approaches to maintaining orreducing oxygen levels in packaged items have been advanced, thereremains a need for improved oxygen-scavenging compositions and packagingmaterials utilizing the same.

[0010] An object of the present invention is to provide improvedoxygen-scavenging compositions and packaging. Another object is toprovide low cost, oxygen-scavenging compositions of improved efficiency.Another object is to provide oxygen-scavenging compositions that can beused effectively, even at relatively low levels, in a wide range ofactive-barrier packaging films and sheets, including laminated andcoextruded multilayer films and sheets. Another object is to provideactive-barrier packaging containers that can increase the shelf-life ofoxygen-sensitive products by slowing the passage of external oxygen intothe container, by absorbing oxygen present inside the container or both.Other objects will be apparent to those skilled in the art.

SUMMARY OF THE INVENTION

[0011] These objects can be attained according to the invention byproviding oxygen-scavenging compositions comprising at least oneoxidizable metal component, at least one electrolyte component and atleast one solid, non-electrolytic acidifying component. Optionally, awater-retentive binder and/or polymeric resin can be included in thecomposition, if desired. For particularly efficient oxygen absorptionand cost effective formulations, the oxidizable metal componentcomprises iron, the electrolyte component comprises sodium chloride andthe solid, non-electrolytic, acidifying component comprises sodium acidpyrophosphate. In one embodiment, the invented compositions are providedin the form of a powder or granules for use in packets. In anotherembodiment, the compositions include or are added to a thermoplasticresin and are used in fabrication of articles by melt processingmethods. Concentrates comprising the compositions or their componentsand at least one thermoplastic resin also are provided and offeradvantages in melt processing operations. For the embodiments thatinclude a thermoplastic resin, thermally stable acidifying componentsare preferred and provide a more aesthetically pleasing film or article.Preferred thermoplastic resins are soft, flexible resins which enablethe oxygen-scavenging composition to absorb oxygen more efficiently. Theinvented compositions also are provided in the form of packagingstructures and components thereof.

[0012] As used herein, the term “electrolyte compound” means a compoundwhich substantially dissociates in the presence of water to formpositive and negative ions. By “solid, non-electrolytic acidifyingcomponent” or, simply, “acidifying component,” is meant a componentcomprising a material which is normally solid and which, in diluteaqueous solution, has a pH less than 7 and disassociates only slightlyinto positive and negative ions.

DESCRIPTION OF THE INVENTION

[0013] The invented compositions are oxygen-scavenging compositions thatexhibit improved oxygen-absorption efficiency relative to known,oxidizable metal-electrolyte systems, such as iron and sodium chloride,as a result of inclusion in the compositions of a non-electrolytic,acidifying component. In the presence of moisture, the combination ofthe electrolyte and the acidifying components promotes reactivity ofmetal with oxygen to a greater extent than does either alone.Consequently, oxygen absorption efficiency of the invented compositionsis greater than that of known compositions. For a given weight ofoxygen-scavenging composition, the invented compositions provide greaterscavenging capability than conventional materials, other things beingequal. Alternatively, less of the invented composition is needed toprovide a given level of oxygen-scavenging capability than ifconventional materials are used, other things being equal.

[0014] Advantageously, when incorporated into thermoplastic resins usedfor making packaging articles and components, the improved efficiency ofthe invented compositions can lead to reductions in not only oxygenscavenger usage but, also, resin usage because the lower loading levelspermitted by the invented compositions facilitate downgauging to thinneror lighter weight packaging structures.

[0015] Another advantage of the invented compositions when used infabrication of articles by melt processing is that one or more of thecomponents of the composition can be provided in the form of aconcentrate in a thermoplastic resin, thereby facilitating convenientuse of the compositions and tailoring of scavenging compositions toparticular product requirements.

[0016] The oxygen-scavenging composition of the present inventioncomprises an oxidizable metal component, an electrolyte component, and asolid, non-electrolytic, acidifying component. Optionally, thecomposition also comprises a water-absorbing binder component. Thecomposition can also comprise a polymeric resin if desired. Thecomposition can be packaged in an enclosure to form a packet suitablefor placement in the interior of a package. The enclosure can be madefrom any suitable material that is permeable to air but not permeable tothe components of the oxygen-scavenging composition or the product to bepackaged to a degree that would allow intermingling of theoxygen-scavenging composition with products with which it might bepackaged. Suitably, the enclosure is constructed of paper orair-permeable plastic. The composition also can be incorporated intopolymeric resins for use in making fabricated articles, for example bymelt processing, spraying and coating techniques.

[0017] Suitable oxidizable metal components comprise at least one metalor compound thereof capable of being provided in particulate or finelydivided solid form and of reacting with oxygen in the presence of theother components of the composition. For compositions to be used inpackaging applications, the component also should be such that, bothbefore and after reaction with oxygen, it does not adversely affectproducts to be packaged. Examples of oxidizable metals include iron,zinc, copper, aluminum, and tin. Examples of oxidizable metal compoundsinclude ferrous sulfate, cuprous chloride and other iron (II) and copper(I) salts as well as tin (II) salts. Mixtures also are suitable.Oxidizable metal components consisting entirely or mostly of reducediron powder are preferred because they are highly effective in terms ofperformance, cost and ease of use.

[0018] The invented compositions also comprise an electrolyte componentand a solid, non-electrolytic, acidifying component. These componentsfunction to promote reaction of the oxidizable metal with oxygen. Whileeither such component promotes oxidation in the absence of the other,the combination is more effective than either alone.

[0019] Suitable electrolyte components comprise at least one materialthat substantially disassociates into positive and negative ions in thepresence of moisture and promotes reactivity of the oxidizable metalcomponent with oxygen. Like the oxidizable metal component, it alsoshould be capable of being provided in granular or powder form and, forcompositions to be used in packaging, of being used without adverselyaffecting products to be packaged. Examples of suitable electrolytecomponents include various electrolytic alkali, alkaline earth andtransition metal halides, sulfates, nitrates, carbonates, sulfites andphosphates, such as sodium chloride, potassium bromide, calciumcarbonate, magnesium sulfate and cupric nitrate. Combinations of suchmaterials also can be used. A particularly preferred electrolytecomponent, both for its cost and performance, is sodium chloride.

[0020] The acidifying component comprises a solid, non-electrolyticcompound that produces an acidic pH, i.e., less than 7, preferably lessthan 5, in dilute aqueous solution. The component disassociates intopositive and negative ions only slightly in aqueous solution. As withthe oxidizable metal and electrolyte components, for compositions to beused in packaging applications, the acidifying component should becapable of being used without adversely affecting products to bepackaged. For applications in which the invented compositions include orare to be used with a thermoplastic resin, the acidifying component alsoshould have sufficient thermal stability to withstand melt compounding,processing, and fabrication into the final article or film. The termthermal stability as used herein means that the acidifying componentdecomposes only insubstantially, if at all, at the normal processingtemperature of the polymer from which the film or article is fabricated.The acidifier is considered to have decomposed when it no longerfunctions for its intended purpose or the films and articles fabricatedfrom the thermoplastic resin contain a significant number of bubbles andvoids due to the loss of water or hydrate. For example, some acidifyingcomponents have a thermal decomposition temperature below typicalthermoplastic processing temperatures. Thus, when these acidifyingcomponents are blended into the polymer they thermally decompose intoanother material and no longer act as an acidifier. Other acidifyingcomponents will not thermally decompose and continue to function asacidifiers, but may lose water or hydrate at higher processingtemperatures. This loss of water or hydrate during fabrication willcause voids or bubbles to appear in the final film or article.

[0021] Suitable materials include various organic and inorganic acidsand their salts. Depending on the end-use application, particular groupsof acidifying components are preferred. For the embodiment directed touse in a packet or sachet, organic acids and their salts can be used.For example citric acid, anhydrous citric acid, citric acid monosodiumsalt, citric acid disodium salt, salicylic acid, ascorbic acid, tartaricacid, ammonium sulfate, ammonium phosphate, nicotinic acid, aluminumammonium sulfate and sodium phosphate monobasic. Combinations of suchmaterials may also be used. These acidifying components are notpreferred for use in resin applications because their thermaldecomposition temperature is below the compounding temperature of commonpackaging resins. The thermal decomposition temperature of some commonorganic acids are as follows: salicylic acid (98° C.); citric acid (175°C.); ascorbic acid (193° C.); and tartaric acid (191° C.).

[0022] When the oxygen-scavenging compositions of the present inventionare compounded into thermoplastic resins such as polyethylene, usingpolymer compounding or melt-fabrication operations, preferred acidifyingcomponents are those that are thermally stable—i.e., do not thermallydecompose and do not lose water or hydrate—at typical film processingtemperatures which range from about 200° C. to about 260° C. Examplesinclude: potassium acid pyrophosphate, calcium acid pyrophosphate,monocalcium phosphate, magnesium sulfate, disodium dihydrogenpyrophosphate, also known as sodium acid pyrophosphate, sodiummetaphosphate, sodium trimetaphosphate, sodium hexametaphosphate,aluminum sulfate and aluminum potassium sulfate. Combinations of thesematerials may also be used. The dehydration temperature of sodium acidpyrophosphate and monocalcium phosphate is 266° C. and 235° C.respectively.

[0023] It has been discovered that although these acidifying componentsare thermally stable at normal resin processing temperatures, they areless stable at higher processing temperatures, such as those used forextrusion coating which range from about 270° C. to about 340° C. Atthese higher processing temperatures some acidifying components liberatewater which creates voids and bubbles in the films and articlesmanufactured. These voids and bubbles give the final films and articlesan unpleasant appearance, and if the voids and bubbles are large enough,may reduce the films ability to scavenge oxygen. In order to obtain theimproved oxygen-scavenging benefits of the acidifying component withoutcompromising the quality of the film, dehydrated derivatives of certainacidifying components are used. Conveniently, dehydration may beaccomplished by calcination in a furnace or kiln. The calcining processdrives off the water from the acidifying component prior to itscompounding and use in a high temperature fabrication operation. In thismanner, the water is not driven off during the extrusion film coatingprocess and the formation of voids and bubbles is prevented. Preferably,no more than 500 ppm of water remain in the oxygen-scavenging resincomposition, and more preferably no more than 100 ppm.

[0024] In addition, the water may be driven off during the initial meltcompounding of the oxygen-scavenging composition to formoxygen-scavenging resin pellets. These pellets are then subsequentlyprocessed or fabricated into the final article or film. Since the wateris driven off during the initial melt-compounding, and not duringfabrication, formation of voids and bubbles in the film or article isavoided.

[0025] For such high temperature extrusion coating process, preferredacidifying components are those that are thermally stable above 270° C.Examples include calcined products of: monocalcium phosphate,monomagnesium phosphate, magnesium sulfate, disodium dihydrogenpyrophosphate, also known as sodium acid pyrophosphate, sodiummetaphosphate, sodium trimetaphosphate, sodium phosphate monobasic,sodium hexametaphosphate, aluminum sulfate, potassium phosphatemonobasic, potassium acid pyrophosphate, aluminum potassium sulfate andcombinations thereof. Sodium metaphosphate, sodium trimetaphosphate, andsodium hexametaphosphate are all intermediates of the sodium acidpyrophosphate calcining process. Extrusion coated packaging films andarticles made from oxygen-scavenging resins containing a metal compound,an electrolyte and a calcined acidifying component, are free of voidsand bubbles and exhibit improved oxygen absorption rates and capacitycompared to those scavenging resins that contain no acidifyingcomponent. The thermal decomposition temperature of calcined monocalciumphosphate is 375° C. and calcined sodium acid pyrophosphate or sodiumhexametaphosphate is 550° C.

[0026] Components of the invented oxygen-scavenging compositions arepresent in proportions effective to provide oxygen-scavenging effects.Preferably, at least one part by weight electrolyte component plusacidifying component is present per hundred parts by weight oxidizablemetal component, with the weight ratio of electrolyte component toacidifying component ranging from about 99:1 to about 1:99. Morepreferably, at least about 10 parts electrolyte plus acidifyingcomponents are present per 100 parts oxidizable metal component topromote efficient usage of the latter for reaction with oxygen. There isno upper limit on the amount of electrolyte plus acidifier relative tometal from this standpoint although little or no gain in oxidationefficiency is seen above about 200 parts per 100 parts metal andeconomic and processing considerations may favor lower levels. In orderto achieve an advantageous combination of oxidation efficiency, low costand ease of processing and handling, about 30 to about 150 partselectrolyte plus acidifying component per 100 parts metal component aremost preferred.

[0027] An optional water-absorbing binder can also be included in theinvented compositions, if desired, to further enhance oxidationefficiency of the oxidizable metal. The binder can serve to provideadditional moisture which enhances oxidation of the metal in thepresence of the promoter compounds. The binder is dry when it is addedto the oxygen-scavenging composition and absorbs moisture from theproducts packages in the final article or during retort. Water-absorbingbinders suitable for use generally include materials that absorb atleast about 5 percent of their own weight in water and are chemicallyinert. Examples of suitable binders include diatomaceous earth,boehmite, kaolin clay, bentonite clay, acid clay, activated clay,zeolite, molecular sieves, talc, calcined vermiculite, activated carbon,graphite, carbon black, and the like. It is also contemplated to utilizeorganic binders, examples including various water absorbent polymers asdisclosed in Koyama et al., European Patent Application No. 428,736.Mixtures of such binders also can be employed. Preferred binders arebentonite clay, kaolin clay, and silica gel. When used, thewater-absorbent binder preferably is used in an amount of at least aboutfive parts by weight per hundred parts by weight of the oxidizablemetal, electrolyte and acidifying components. More preferably, about 15to about 100 parts of binder per hundred parts metal are present aslesser amounts may have little beneficial effect while greater amountsmay hinder processing and handling of the overall compositions withoutoffsetting gain in oxygen-scavenging performance. When a bindercomponent is used in compositions compounded into plastics, the bindermost preferably is present in an amount ranging from about 10 to about50 parts per hundred parts metal to enhance oxidation efficiency atloading levels low enough to ensure ease of processing.

[0028] A particularly preferred oxygen-scavenging composition accordingto the invention comprises iron powder as the metal component, sodiumchloride as the electrolyte and sodium acid pyrophosphate or monocalciumphosphate as the acidifying component, with about 10 to about 150 partsby weight sodium chloride plus sodium acid pyrophosphate or monocalciumphosphate being present per hundred parts by weight iron and the weightratio of sodium chloride to sodium acid pyrophosphate or monocalciumphosphate being about 10:90 to about 90:10. Optionally, up to about 100parts by weight water absorbing binder per hundred parts by weight ofthe other components also are present. Most preferably, the compositioncomprises iron powder, about 5 to about 100 parts sodium chloride andabout 5 to about 70 parts sodium acid pyrophosphate per hundred partsiron and up to about 50 parts binder per hundred parts of the othercomponents.

[0029] According to another aspect of this invention, there is providedan oxygen scavenger resin composition comprising at least one plasticresin and the above-described oxygen-scavenging composition, with orwithout the water-absorbent binder component. The selection of theacidifying component will depend on the melt fabrication temperature ofthe plastic resin. Sodium acid pyrophosphate and monocalcium phosphateare thermally stable above 200° C., while calcined products of sodiumacid pyrophosphate and calcined products of monocalcium phosphate arestable above 270° C.

[0030] Any suitable polymeric resin into which an effective amount ofthe oxygen-scavenging composition of this invention can be incorporatedand that can be formed into a laminar configuration, such as film, sheetor a wall structure, can be used as the plastic resin in thecompositions according to this aspect of the invention. Thermoplasticand thermoset resins can be used. Examples of thermoplastic polymersinclude polyamides, such as nylon 6, nylon 66 and nylon 612, linearpolyesters, such as polyethylene terephthalate, polybutyleneterephthalate and polyethylene naphthalate, branched polyesters,polystyrenes, styrene block copolymers such as those comprising styreneblocks and rubber blocks comprising ethylene, propylene, isoprene,butadiene, butylene or isobutylene polymer blocks or combinationsthereof, polycarbonate, polymers of unsubstituted, substituted orfunctionalized olefins such as polyvinyl chloride, polyvinylidenedichloride, polyacrylamide, polyacrylonitrile, polyvinyl acetate,polyacrylic acid, polyvinyl methyl ether, ethylene vinyl acetatecopolymer, ethylene methyl acrylate copolymer, polyethylenes (including,high, low, and linear low density polyethylenes and so-calledmetallocene polyethylenes), polypropylene, ethylene-propylenecopolymers, poly(1-hexene), poly(4-methyl-1-pentene), poly(1-butene),poly(3-methyl-1-butene), poly(3-phenyl-1-propene) andpoly(vinylcyclohexane). Homopolymers and copolymers are suitable as arepolymer blends containing one or more of such materials. Thermosettingresins, such as epoxies, oleoresins, unsaturated polyester resins andphenolics also are suitable.

[0031] Preferred polymers are thermoplastic resins having oxygenpermeation coefficients greater than about 2×10⁻¹² cc-cm/cm²-sec-cm Hgas measured at a temperature of 20° C. and a relative humidity of 0%because such resins are relatively inexpensive, easily formed intopackaging structures and, when used with the invented oxygen-scavengingcompositions, can provide a high degree of active barrier protection tooxygen-sensitive products. Examples of these include polyethyleneterephthalate and polyalpha-olefin resins such as high, low and linearlow density polyethylene and polypropylene. Even relatively low levelsof oxygen-scavenging composition, e.g., about 5 to about 15 parts perhundred parts resin, can provide a high degree of oxygen barrierprotection to such resins. Among these preferred resins, permeability tooxygen increases in the order polyethylene terephthalate (“PET”),polypropylene (“PP”), high density polyethylene (“HDPE”), linear lowdensity polyethylene (“LLDPE”), and low density polyethylene (“LDPE”),other things being equal. Accordingly, for such polymeric resins, oxygenscavenger loadings for achieving a given level of oxygen barriereffectiveness increase in like order, other things being equal.

[0032] According to a preferred embodiment of the invention, thethermoplastic resin comprises a soft resin with a flexible molecularchain. Such soft resins with the flexibility of rubber, such aspolyalpha-olefins polymerized using metallocene catalysts (also known asplastomers) and thermoplastic elastomers, show unexpectedly superioroxygen absorption efficiency when compared to more rigid thermoplasticresins, all other conditions being equal. It is believed that theflexible molecular structure of soft resins facilitates the migrationand intimate contact of the oxygen-scavenging components. This closecontact promotes the oxidation reaction which leads to unexpectedlyhigher oxygen absorption efficiency (cc O₂/gm Fe) compared to harder andmore rigid polymeric resins. The softness and flexibility of a resin canbe determined by examining several properties including its 1% secantmodulus (ASTM D 882-3) and its Shore Hardness (ASTM D 2240). Measuringeither of the properties will provide a good indication of whether aresin will exhibit improved oxygen efficiency. Typically, improvedoxygen absorption efficiency can be found in resins with a 1% secantmodulus less than 25,000 p.s.i. and/or a Shore D Hardness less than 45.Preferred resins have a 1% secant modulus less than about 20,000 p.s.i.and/or a Shore D Hardness less than about 42. Sample carrier resins,their secant modulus and Shore Hardness are listed in Example 11, TableII.

[0033] Preferred, soft, flexible resins according to this embodiment ofthe invention are polyalpha-olefins polymerized using metallocenecatalysts such as metallocene polyethylenes (“mPE”) and metallocenepolypropylenes (“mPP”). mPEs are copolymers of ethylene with at leastone higher alpha-olefin of about 4-8 carbons such as butene, hexene andoctene with comonomer levels from about 1-25%. mPEs also have a narrowmolecular weight distribution—(MW)_(W)/(MW)_(n)—of about 2 to 5.Specific examples include Dow Affinity resins, Dow/Dupont Engage resinsand Exxon Exact resins. These mPEs are described in the literature aslinear, short chain branched polymer chains with high comonomer content,narrow comonomer distribution and uniform, narrow molecular weightdistribution. The 1% secant modulus range for mPEs is about 2,500 toabout 9,000 p.s.i., and the Shore D Hardness from about 29 to about 41.By contrast, the conventional multi-site Zieglar-Natta-catalyzedpolyolefins (e.g. “LLDPE”) are linear with broad comonomer distributionand broader molecular weight distribution of about 6 to 8, andtraditional radical-initiated polyolefins (e.g. “LDPE”) contain nocomonomers, are highly branched with long and short chain branches, andhave a broad molecular weight distribution of about 10 to 14.Conventional LDPE resins have a 1% secant modulus from about 25,000p.s.i. to about 38,000 p.s.i. and a Shore D Hardness from about 45-55.LLDPE resins have a 1% secant modulus from about 30,000 to about 75,000and a Shore D Hardness from about 45-55. Polypropylene has a 1% secantmodulus range from about 160,000 to about 230,000 p.s.i. and a Shore DHardness from about 65 to about 85. As carrier resins for theoxygen-scavenging component, mPEs have shown superior oxygen absorptionrates and capacities relative to oxygen scavenger carrier resinscomprising conventional LDPE, LLDPE and PP.

[0034] Another group of preferred, soft, flexible resins that showimproved oxygen absorption efficiency are styrene block copolymers suchas those comprising styrene blocks and rubber blocks of ethylene,propylene, isoprene, butadiene, butylene or isobutylene or combinationsthereof. (“styrene-rubber block copolymers”). Styrene-rubber blockcopolymers consist of block segments of polymerized styrene monomerunits and rubber monomer units such as butadiene, isoprene andethylene-butylene. The styrene/rubber ratio in the copolymers can varywidely, but typically from 15-40 parts styrene blocks to 60-85 partsrubber blocks. The rubber units give these block copolymers theirflexibility and elasticity. The 1% secant modulus of these blockcopolymers is from about 150 to about 2000 p.s.i. Their Shore D Hardnessis from about 5 to about 15. As suggested above, this flexibility andsoftness facilitates migration and intimate contact between theoxygen-scavenging components—i.e., the oxidizable metal component,electrolyte component and solid, non-electrolytic, acidifyingcomponent—which promotes the efficient oxidation of the metal component.

[0035] A specific example of such block copolymers are Shell's G and Dseries Kraton® rubber polymers which are soft, flexible, elastic,thermoplastics. Shell's G series Kraton® consists ofstyrene-ethylene-butylene-styrene block copolymers (“SEBS”), and the Dseries consists of styrene-butadiene-styrene block copolymer (“SBS”).Another example is a styrene-isobutylene-styrene block copolymer(“SIBS”).

[0036] In addition to metallocene-catalyzed polyolefins andstyrene-rubber block copolymers, soft, flexible resins such as very lowdensity polyethylene (“VLDPE”), ultra low density polyethylene(“ULDPE”), elastomeric forms of polypropylene such as elastomerichomopolypropylene (“EHPP”), and elastomeric copolymer polypropylene canalso be used as the carrier resin to enhance oxygen absorptionefficiency. ULDPE and VLDPE have a 1% secant modulus from about 18,000to about 20,000 p.s.i. and a Shore D Hardness of about 42. Elastomericforms of PP have a Shore D of about 20 and 1% secant modulus of about1,800 p.s.i. Selection of the polymeric resin will depend upon severalfactors including the end-use packaging application, the level of oxygenabsorption required, and whether or not the oxygen-scavengingcomposition in the polymeric resin will be further blended with the sameor distinct resin.

[0037] In selecting a thermoplastic resin for use or compounding withthe oxygen-scavenging composition of the invention, the presence ofresidual antioxidant compounds in the resin can be detrimental to oxygenabsorption effectiveness. Phenol-type antioxidants and phosphite-typeantioxidants are commonly used by polymer manufacturers for the purposeof enhancing thermal stability of resins and fabricated productsobtained therefrom. Specific examples of these residual antioxidantcompounds include materials such as butylated hydroxytoluene,tetrakis(methylene(3,5-di-t-butyl4-hydroxyhydro-cinnamate)methane andtriisooctyl phosphite. Such antioxidants are not to be confused with theoxygen scavenger components utilized in the present invention.Generally, oxygen absorption of the scavenger compositions of thepresent invention is improved as the level of residual antioxidantcompounds is reduced. Thus, commercially available resins containing lowlevels of phenol-type or phosphite-type antioxidants, preferably lessthan about 1600 ppm, and most preferably less than about 800 ppm, byweight of the resin, are preferred (although not required) for use inthe present invention. Examples are Dow Chemical Dowlex 2032 linear lowdensity polyethylene (LLDPE); Union Carbide GRSN 7047 LLDPE; GoodyearPET “Traytuf” 9506; and Eastman PETG 6763. Commercially available mPEssuch as Exxon Exact, Dow Affinity, and Dow/Dupont Engage have acceptablelevels of antioxidants and styrene-rubber block copolymers such asKraton® have suitable levels as well. Measurement of the amount ofresidual antioxidant can be performed using high pressure liquidchromatography.

[0038] When used in combination with resins, the oxidizable metal,electrolyte and acidifying components of the invented oxygen-scavengingcompositions, and any optional water-absorbent binder that may be used,are used in particulate or powder form. Particle sizes of 50 mesh orsmaller are preferred to facilitate melt-processing of oxygen scavengerthermoplastic resin formulations. For use with thermoset resins forformation of coatings, particle sizes smaller than the thickness of thefinal coating are employed. The oxygen scavenger can be used directly inpowder or particulate form, or it can be processed, for example by meltcompounding or compaction-sintering, into pellets to facilitate furtherhandling and use.

[0039] Processing aids may also be used when the oxygen scavengingcomponents are combined with resins. For example, flouropolymers such asDynamar FX-9613 and FX-5920A available from Dyneon can be added to themelt compounding process to reduce the melt fracture of the polymermatrix and possibly reduce the die pressure. Preferably, 50 ppm-5000 ppmof flouropolymer may be added, more preferably 200 ppm-2000 ppm, andmost preferably 500 ppm-1000 ppm of flouropolymer may be added to theoxygen-scavenging resin comprised of oxidizable metal, electrolyte,acidifying component, and the carrier resin of the present invention.

[0040] The mixture of oxidizable metal component, electrolyte component,acidifying component and optional water-absorbent binder can be addeddirectly to a thermoplastic polymer compounding or melt-fabricationoperation, such as in the extrusion section thereof, after which themolten mixture can be advanced directly to a film or sheet extrusion orcoextrusion line to obtain monolayer or multilayer film or sheet inwhich the amount of oxygen-scavenging composition is determined by theproportions in which the composition and resin are combined in the resinfeed section of the extrusion-fabrication line. Alternatively, themixture of oxidizable metal component, electrolyte component, acidifyingcomponent and optional binder can be compounded into masterbatchconcentrate pellets, which can be further let down into packaging resinsfor further processing into extruded film or sheet, or injection moldedarticles such as tubs, bottles, cups, trays and the like. Soft, flexibleresins with a 1 % Secant modulus less than 25,000 p.s.i. and a Shore DHardness less than 45 are more preferred carrier resins for theconcentrate pellets because they promote greater oxygen absorptionefficiency when used in combination with more rigid packaging resins.Soft, flexible resins with a 1% Secant modulus less than about 20,000p.s.i. and a Shore D Hardness less than about 42 are particularlypreferred. Again, examples of such resins include mPEs, styrene-rubberblock copolymers, VLDPE, ULDPE, and elastomeric forms of polypropylene.Particularly preferred carrier resins are styrene-butadiene blockcopolymers and metallocene polyethylenes.

[0041] The degree of mixing of oxidizable metal, electrolyte andacidifying components and, if used, optional binder component has beenfound to affect oxygen absorption performance of the oxygen-scavengingcompositions, with better mixing leading to better performance. Mixingeffects are most noticeable at low electrolyte plus acidifyingcomponents to oxidizable metal component ratios and at very low and veryhigh acidifying component to electrolyte component ratios. Below about10 parts by weight electrolyte plus acidifying components per hundredparts by weight metal component, or when the weight ratio of either theelectrolyte or acidifying component to the other is less than about10:90, the oxygen scavenger components are preferably mixed by aqueousslurry mixing followed by oven drying and grinding into fine particles.Below these ratios, mixing by techniques suitable at higher ratios, suchas by high-intensity powder mixing, as in a Henschel mixer or a Waringpowder blender, or by lower intensity mixing techniques, as in acontainer on a roller or tumbler, may lead to variability in oxygenuptake, particularly when the compositions are incorporated intothermoplastic resins and used in melt processing operations. Otherthings being equal, it has been found that oxygen-scavengingcompositions prepared by slurry mixing have the highest oxygenabsorption efficiency or performance, followed in order by compositionsprepared using high intensity solids mixers and roller/tumbler mixingtechniques. However, when mixing a composition containing a calcinedacidifying component for use in a high temperature application,non-slurry mixing techniques are preferred.

[0042] Other factors that may affect oxygen absorption performance ofthe invented oxygen-scavenging compositions include surface area ofarticles incorporating the compositions, with greater surface areanormally providing better oxygen absorption performance. The amount ofresidual moisture in the water-absorbent binder, if used, also canaffect performance with more moisture in the binder leading to betteroxygen absorption performance. However, there are practical limits onthe amount of moisture that should be present in the binder because toomuch can cause premature activation of the oxygen scavenger compositionas well as processing difficulties. The moisture can also cause pooraesthetics, such as bubbles and voids, in fabricated products.Especially those fabricated at high temperatures.

[0043] When incorporated into thermoplastic resins and used forfabrication of articles by melt processing techniques, the nature of theresin also can have a significant effect. Thus when the inventedoxygen-scavenging compositions are used with amorphous and/or oxygenpermeable polymers such as polyolefins or amorphous polyethyleneterephthalate, higher oxygen absorption is seen than when thecompositions are used with crystalline and/or oxygen barrier polymerssuch as crystalline polyethylene terephthalate and EVOH. Superior oxygenabsorption efficiency is observed when the invented compositions areused with soft, flexible resins such as metallocene catalyzedpolyolefins and styrene-rubber block copolymers.

[0044] When used with thermoplastic resins, the oxygen-scavengingcompositions can be incorporated directly into the resin in amountseffective to provide the desired level of oxygen-scavenging ability.When so-used, preferred oxygen scavenger levels will vary depending onthe choice of resin, configuration of the article to be fabricated fromthe resin and oxygen-scavenging capability needed in the article. Use ofresins with low inherent viscosity, e.g., low molecular weight resins,normally permits higher loadings of scavenger composition without lossof processability. Conversely, lesser amounts of oxygen scavenger mayfacilitate use of polymeric materials having higher viscosities.Preferably, at least about 2 parts by weight oxygen-scavengingcomposition are used per 100 parts by weight resin. Loading levels aboveabout 200 parts per hundred parts resin generally do not lead to gainsin oxygen absorption and may interfere with processing and adverselyaffect other product properties. More preferably, loading levels ofabout 5 to about 150 parts per hundred are used to obtain goodscavenging performance while maintaining processability. Loading levelsof about 5 to about 15 parts per hundred are particularly preferred forfabrication of thin films and sheets. For films and sheets made directlyfrom resin concentrates, loading levels of about 5 to about 100 partsoxygen-scavenging composition per hundred parts resin are preferred, 5to 50 parts most preferred.

[0045] Preferred oxygen scavenger resin compositions for fabrication ofpackaging articles comprise at least one thermoplastic resin and about 5to about 150 parts by weight oxygen-scavenging composition per hundredparts by weight resin, more preferably 5 to about 50 parts, with theoxygen-scavenging composition comprising iron powder, sodium chlorideand sodium acid pyrophosphate. About 10 to about 200 parts by weightsodium chloride and sodium acid pyrophosphate per hundred parts byweight iron are present in the scavenging composition, more preferablyabout 30 to about 130 parts and the weight ratio of sodium chloride tosodium acid pyrophosphate is about 10:90 to about 90:10. Up to about 50parts by weight water-absorbent binder per hundred parts by weight ofresin and oxygen scavenger also can be included. Especially preferredcompositions of this type comprise polypropylene, high, low or linearlow density polyethylene or polyethylene terephthalate as the resin,about 5 to about 30 parts by weight oxygen scavenger per hundred partsby weight resin, about 5 to about 100 parts by weight sodium chlorideand about 5 to about 70 parts by weight sodium acid pyrophosphate perhundred parts by weight iron and up to about 50 parts by weight binderper hundred parts by weight iron plus sodium chloride plus sodium acidpyrophosphate.

[0046] Another preferred composition for packaging articles comprises asoft, flexible resin such as mPE or a styrene-rubber block copolymer,and about 5 to about 150 parts by weight oxygen scavenger per hundredparts by weight resin, with the oxygen-scavenging composition comprisingiron powder, sodium chloride and sodium acid pyrophosphate ormonocalcium phosphate. The oxygen scavenger is about 5 to about 150parts by weight sodium chloride and about 5 to about 100 parts by weightsodium acid pyrophosphate or monocalcium phosphate per hundred parts byweight iron.

[0047] When packaging articles are manufactured using a high temperaturefabrication process, use of calcined sodium acid pyrophosphate orcalcined monocalcium phosphate as acidifying components are preferred toprevent the formation of bubbles and voids in the fabricated article.

[0048] While the oxygen-scavenging composition and resin can be used ina non-concentrated form for direct fabrication of scavenging sheets orfilms (i.e., without further resin dilution), it also is beneficial touse the oxygen-scavenging composition and resin in the form of aconcentrate. When so-used, the ability to produce a concentrate with lowmaterials cost weighs in favor of relatively high loadings of scavengerthat will still permit successful melt compounding, such as by extrusionpelletization. Thus concentrate compositions according to the inventionpreferably contain at least about 10 parts by weight oxygen-scavengingcomposition per hundred parts by weight resin and more preferably about30 to about 150 parts per hundred. Suitable resins for suchoxygen-scavenging concentrate compositions include any of thethermoplastic polymer resins described herein. Low melt viscosity resinsfacilitate use of high scavenger loadings and typically are used insmall enough amounts in melt fabrication of finished articles that thetypically lower molecular weight of the concentrate resin does notadversely affect final product properties. Preferred carrier resins arepolypropylene, high density, low density and linear low densitypolyethylenes, and polyethylene terephthalate. Preferred among those arepolypropylenes having melt flow rates (ASTM D1238) of about 1 to about40 g/10 min, polyethylenes having melt indices (ASTM D1238) of about 1to about 20 g/10 min and polyethylene terephthalates having inherentviscosities (ASTM D2857) of about 0.6 to about 1 inphenol/trichloroethane.

[0049] A most preferred carrier resin for the concentrate compositionsare the soft, flexible resins as indicated by a Shore D Hardness lessthan 45 andlor a secant modulus less than 25,000 p.s.i. Particularlypreferred are those resins with a 1% Secant modulus less than about20,000 p.s.i. and a Shore D Hardness less than about 42. Theseconcentrate resins preferably contain about 30 to about 150 parts byweight oxygen-scavenging component per hundred parts by weight resin andmost preferably about 75 to about 125 parts by weight oxygen-scavengingcomposition per 100 parts by weight resin. The oxygen-scavengingcomposition is preferably about 25 to 125 parts by weight sodiumchloride and about 25 to 75 parts by weight acidifying componentselected from sodium acid pyrophosphate, monocalcium phosphate, calcinedsodium acid pyrophosphate or calcined monocalcium phosphate per 100parts by weight iron. For fabrication of thin films from theseconcentrates, loading levels of about 5 -150 parts oxygen-scavengingcomposition to 100 parts resin is preferred, and about 10 -100 partsoxygen-scavenging composition to hundred parts resin is more preferred,and 10 -50 parts oxygen-scavenging composition to hundred parts resin ismost preferred. Concentrates and films produced in accordance with theabove, exhibit superior oxygen absorption capabilities.

[0050] When concentrates are used to fabricate oxygen-scavenging filmsand packaging articles, such concentrates can be used alone or incombination with a thermoplastic resin that is either the same ordistinct from the carrier resin. Thus, the concentrate can be comprisedof a soft flexible resin and the film resin selected from polypropylene,polyethylene, polyethylene terephthalate or any other suitable resindepending on the final packaging structure. Likewise, both the carrierresin and the film or packaging resin can be comprised of the same ordistinct soft, flexible resin or the same or distinct more rigidthermoplastic resin. Preferably, at least the carrier resin is of thesoft, flexible type to achieve superior oxygen absorption capabilities.

[0051] It also is contemplated to utilize various components of theoxygen-scavenging composition or combinations of such components to formtwo or more concentrates that can be combined with a thermoplastic resinand fabricated into an oxygen-scavenging product. An advantage of usingtwo or more concentrates is that the electrolyte and acidifyingcomponents can be isolated from the oxidizable metal until preparationof finished articles, thereby preserving full or essentially fulloxygen-scavenging capability until actual use and permitting lowerscavenger loadings than would otherwise be required. In addition,separate concentrates permit more facile preparation of differingconcentrations of the electrolyte and acidifying components and/or waterabsorbent binder with the oxidizable metal and also enable fabricatorsto conveniently formulate a wide range of melt-processible resincompositions in which oxygen-scavenging ability can be tailored tospecific end use requirements. Preferred components or combinations ofcomponents for use in separate concentrates are (1) acidifyingcomponent; (2) combinations of oxidizable metal component with waterabsorbing binder component; and (3) combinations of electrolyte andacidifying components.

[0052] A particularly preferred component concentrate is a compositioncomprising an acidifying component such as sodium acid pyrophosphate,monocalcium phosphate, calcined sodium acid pyrophosphate or calcinedmonocalcium phosphate and a thermoplastic resin. Such a concentrate canbe added in desired amounts in melt fabrication operations utilizingthermoplastic resin that already contains, or to which will be added,other scavenging components, such as an oxidizable metal or combinationthereof with an electrolyte, to provide enhanced oxygen-scavengingcapability. Especially preferred are concentrates containing about 10 toabout 150 parts by weight sodium acid pyrophosphate, calcined sodiumacid pyrophosphate, or calcined monocalcium phosphate per hundred partsby weight resin. The concentrate resin may be selected from any numberof resins such as with polypropylene, polyethylene and polyethyleneterephthalate, with soft flexible resins being the most preferred withmPEs and styrene-rubber block copolymers giving the best results.

[0053] Polymeric resins that can be used for incorporating theoxygen-scavenging compositions into internal coatings of cans via spraycoating and the like are typically thermoset resins such as epoxy,oleoresin, unsaturated polyester resins or phenolic based materials.

[0054] This invention also provides articles of manufacture comprisingat least one melt-fabricated layer incorporating the oxygen-scavengingcompositions as described above. Because of the improved oxidationefficiency afforded by the invented oxygen-scavenging compositions, thescavenger-containing layer can contain relatively low levels of thescavenger. The articles of the present invention are well suited for usein flexible or rigid packaging structures. In the case of rigid sheetpackaging according to the invention, the thickness of theoxygen-scavenging layer is preferably not greater than about 100 mils,and is most preferably in the range of about 10 to about 50 mils. In thecase of flexible film packaging according to the invention, thethickness of the oxygen scavenger layer is preferably not greater thanabout 10 mils and, most preferably, about 0.5 to about 8 mils. As usedherein, the term “mils” is used for its common meaning, i.e.,one-thousandth of an inch. Packaging structures and fabricated articlesaccording to the invention can be in the form of films or sheets, bothrigid and flexible, as well as container or vessel walls and liners asin trays, cups, bowls, bottles, bags, pouches, boxes, films, cap liners,can coatings and other packaging constructions. Both monolayer andmultilayer structures are contemplated.

[0055] The oxygen-scavenging composition and resin of the presentinvention afford active-barrier properties in articles fabricatedtherefrom and can be melt processed by any suitable fabricationtechnique into packaging walls and articles having excellent oxygenbarrier properties without the need to include layers of costly gasbarrier films such as those based on EVOH, PVDC, metallized polyolefinor polyester, aluminum foil, silica coated polyolefin and polyester,etc. The oxygen scavenger articles of the present invention also providethe additional benefit of improved recyclability. Scrap or reclaim fromthe oxygen-scavenging resin can be easily recycled back into plasticproducts without adverse effects. In contrast, recycle of EVOH or PVDCgas barrier films may cause deterioration in product quality due topolymer phase separation and gelation occurring between the gas barrierresin and other resins making up the product. Nevertheless, it also iscontemplated to provide articles, particularly for packagingapplications, with both active and passive oxygen barrier propertiesthrough use of one or more passive gas barrier layers in articlescontaining one or more active barrier layers according to the invention.Thus, for some applications, such as packaging for food forinstitutional use and others calling for long shelf-life, anoxygen-scavenging layer according to the present invention can be usedin conjunction with a passive gas barrier layer or film such as thosebased on EVOH, PVDC, metallized polyolefins or aluminum foil.

[0056] The present invention is also directed to a packaging wallcontaining at least one layer comprising the oxygen-scavengingcomposition and resin described above. It should be understood that anypackaging article or structure intended to completely enclose a productwill be deemed to have a “packaging wall,” as that term is used herein,if the packaging article comprises a wall, or portion thereof, that is,or is intended to be, interposed between a packaged product and theatmosphere outside of the package and such wall or portion thereofcomprises at least one layer incorporating the oxygen-scavengingcomposition of the present invention. Thus, bowls, bags, liners, trays,cups, cartons, pouches, boxes, bottles and other vessels or containerswhich are intended to be sealed after being filled with a given productare covered by the term “packaging wall” if the oxygen-scavengingcomposition of the invention is present in any wall of such vessel (orportion of such wall) which is interposed between the packaged productand the outside environment when the vessel is closed or sealed. Oneexample is where the oxygen-scavenging composition of the invention isfabricated into, or between, one or more continuous thermoplastic layersenclosing or substantially enclosing a product. Another example of apackaging wall according to the invention is a monolayer or multilayerfilm or sheet containing the present oxygen-scavenging composition usedas a cap liner in a beverage bottle (i.e., for beer, wine, fruit juices,etc.) or as a wrapping material.

[0057] An attractive active-barrier layer is generally understood as onein which the kinetics of the oxidation reaction are fast enough, and thelayer is thick enough, that most of the oxygen permeating into the layerreacts without allowing a substantial amount of the oxygen to transmitthrough the layer. Moreover, it is important that this “steady state”condition exist for a period of time appropriate to end use requirementsbefore the scavenger layer is spent. The present invention affords thissteady state, plus excellent scavenger longevity, in economicallyattractive layer thicknesses, for example, less than about 100 mils inthe case of sheets for rigid packaging, and less than about 10 mils inthe case of flexible films. For rigid sheet packaging according to thepresent invention, an attractive scavenger layer can be provided in therange of about 10 to about 30 mils, while for flexible film packaging,layer thicknesses of about 0.5 to about 8 mils are attractive. Suchlayers can function efficiently with as little as about 2 to about 10weight % oxygen scavenger composition based on weight of the scavengerlayer.

[0058] In fabrication of packaging structures according to theinvention, it is important to note that the oxygen-scavenging resincomposition of the invention is substantially inactive with respect tochemical reaction with oxygen so long as the water activity of thecomposition is less than about 0.2-0.3. In contrast, the compositionbecomes active for scavenging oxygen when the water activity is at orabove about 0.2-0.3. Water activity is such that, prior to use, theinvented packaging articles can remain substantially inactive inrelatively dry environments without special steps to maintain lowmoisture levels. However, once the packaging is placed into use, mostproducts will have sufficient moisture to activate the scavengercomposition incorporated in the walls of the packaging article. In thecase of a hypothetical packaging article according to the inventionhaving an intermediate oxygen-scavenging layer sandwiched between innerand outer layers, the scavenging layer of the structure, in which theoxygen-scavenging composition of the present invention is contained,will be active for chemical reaction with oxygen permeating into thescavenging layer if the following equation is satisfied:$a = {\frac{{{d_{i}({WVTR})}_{o}a_{o}} + {{d_{o}({WVTR})}_{i}a_{i}}}{{d_{i}({WVTR})}_{o} + {d_{o}({WVTR})}_{i}} \geq {0.2 - 0.3}}$

[0059] where:

[0060] d_(i) is the thickness in mils of the inner layer;

[0061] d_(o) is the thickness in mils of the outer layer;

[0062] a_(o) is the water activity of the environment outside thepackaging article (i.e., adjacent the outer layer);

[0063] a_(i) is the water activity of the environment inside thepackaging article (i.e., adjacent the inner layer);

[0064] a is the water activity of the scavenging layer; (WVTR)_(o) isthe water vapor transmission rate of the outer layer of the packagingwall in gm.mil/100 in. sq.day at 100° F. and 90% RH according to ASTME96; and

[0065] (WVTR)_(i) is the water vapor transmission rate of the innerlayer of the packaging wall in gm.mil/100 in. sq. day at 100° F. and 90%RH according to ASTM E96.

[0066] For monolayer packaging constructions in which a layerincorporating the oxygen-scavenging composition is the only layer of thepackaging wall, the package will be active for oxygen absorptionprovided a_(o) or a_(i) is greater than or equal to about 0.2-0.3.

[0067] To prepare a packaging wall according to the invention, anoxygen-scavenging resin formulation is used or the oxygen-scavengingcomposition, or its components or concentrates thereof, is compoundedinto or otherwise combined with a suitable packaging resin whereupon theresulting resin formulation is fabricated into sheets, films or othershaped structures. Formulations or concentrates using soft, flexibleresins as the carrier resin may be compounded or combined with anysuitable packaging resin including but not limited to polypropylene,polyethylene, or polyethylene terephthalate. Extrusion, coextrusion,blow molding, injection molding, extrusion coating and any other sheet,film or general polymeric melt-fabrication technique can be used. Sheetsand films obtained from the oxygen scavenger composition can be furtherprocessed, e.g. by coating or lamination, to form multilayered sheets orfilms, and then shaped, such as by thermoforming or other formingoperations, into desired packaging walls in which at least one layercontains the oxygen scavenger. Such packaging walls can be subjected tofurther processing or shaping, if desired or necessary, to obtain avariety of active-barrier end-use packaging articles. The presentinvention reduces the cost of such barrier articles in comparison toconventional articles which afford barrier properties using passivebarrier films.

[0068] As a preferred article of manufacture, the invention provides apackaging article comprising a wall, or combination of interconnectedwalls, in which the wall or combination of walls defines an enclosableproduct-receiving space, and wherein the wall or combination of wallscomprises at least one wall section comprising an oxygen-scavenginglayer comprising (i) a polymeric resin, preferably a thermoplastic resinor a thermoset resin, most preferably a thermoplastic resin selectedfrom the group consisting of polyolefins, polystyrenes and polyesters,and most preferably soft, flexible resins with a 1% secant modulus lessthan 25,000 p.s.i. and Shore D Hardness less than 45; (ii) an oxidizablemetal preferably comprising at least one member selected from the groupconsisting of iron, copper, aluminum, tin and zinc, and most preferablyabout 1 to about 100 parts iron per hundred parts by weight of theresin; (iii) an electrolyte component and (iv) a solid,non-electrolytic, acidifying component which in the presence of waterhas a pH of less than 7, with about 5 to about 150 parts by weight ofelectrolyte and acidifying components per hundred parts by weight ironpreferably being present and the weight ratio of the acidifyingcomponent to electrolyte component preferably being about 5/95 to about95/5; and, optionally, a water-absorbent binder. In such articles,sodium chloride is the most preferred electrolyte component and sodiumacid pyrophosphate is most preferred as the acidifying component, withthe weight ratio of sodium acid pyrophosphate to sodium chloride mostpreferably ranging from about 10/90 to about 90/10. For articles made byhigh temperature extrusion coating process, calcined sodium acidpyrophosphate or calcined monocalcium phosphate are the most preferredacidifying component.

[0069] A particularly attractive packaging construction according to theinvention is a packaging wall comprising a plurality of thermoplasticlayers adhered to one another in bonded laminar contact wherein at leastone oxygen-scavenging layer is adhered to one or more other layers whichmay or may not include an oxygen-scavenging composition. It isparticularly preferred, although not required, that the thermoplasticresin constituting the major component of each of the layers of thepackaging wall be the same, so as to achieve a “pseudo-monolayer”. Sucha construction is easily recyclable.

[0070] An example of a packaging article using the packaging walldescribed above is a two-layer or three-layer dual ovenable tray made ofcrystalline polyethylene terephthalate (“C-PET”) suitable for packagingpre-cooked single-serving meals. In a three-layer construction, anoxygen-scavenging layer of about 10 to 20 mils thickness is sandwichedbetween two non-scavenging C-PET layers of 3 to 10 mils thickness. Theresulting tray is considered a “pseudo-monolayer” because, for practicalpurposes of recycling, the tray contains a single thermoplastic resin,i.e., C-PET. Scrap from this pseudo-monolayer tray can be easilyrecycled because the scavenger in the center layer does not detract fromrecyclability. In the C-PET tray, the outer, non-scavenging layerprovides additional protection against oxygen transmission by slowingdown the oxygen so that it reaches the center layer at a sufficientlyslow rate that most of the ingressing oxygen can be absorbed by thecenter layer without permeating through it. The optional innernon-scavenging layer acts as an additional barrier to oxygen, but at thesame time is permeable enough that oxygen inside the tray may pass intothe central scavenging layer. It is not necessary to use a three layerconstruction. For example, in the above construction, the inner C-PETlayer can be eliminated. A tray formed from a single oxygen-scavenginglayer is also an attractive construction.

[0071] The pseudo-monolayer concept can be used with a wide range ofpolymeric packaging materials to achieve the same recycling benefitobserved in the case of the pseudo-monolayer C-PET tray. For example, apackage fabricated from polypropylene or polyethylene can be preparedfrom a multilayer packaging wall (e.g., film) containing theoxygen-scavenging composition of the present invention. In a two-layerconstruction the scavenger layer can be an interior layer with anon-scavenging layer of polymer on the outside to provide additionalbarrier properties. A sandwich construction is also possible in which alayer of scavenger-containing resin, such, as polyethylene, issandwiched between two layers of non-scavenging polyethylene.Alternatively, polypropylene, polystyrene or another suitable resin canbe used for all of the layers.

[0072] Another example of a packaging article according to the inventionis a film or packaging wall fabricated from low density polyethylene,polypropylene, PET or any other suitable resin and an oxygen-scavengingconcentrate of a soft, flexible resin such as mPE or styrene-rubberblock copolymers. For example, oxygen-scavenging concentrate pelletscomprised of mPE can be melt-blended with LDPE resin to form a film ofLDPE with regions of mPE which contain the oxygen-scavengingcomposition. Alternatively, oxygen-scavenging concentrate pelletscomprised of styrene-butadiene block copolymer can be melt-blended withPET for form a package wall of PET with regions of styrene-butadieneblock copolymer which contain the oxygen-scavenging composition. In thismanner, the film or package wall can be composed of whatever resin isrequired for the particular packaging application without sacrificingthe superior oxygen absorption capabilities of the soft flexible resins.

[0073] Various modes of recycle may be used in the fabrication ofpackaging sheets and films according to the invention. For example, inthe case of manufacturing a multilayer sheet or film having a scavengingand non-scavenging layer, reclaim scrap from the entire multilayer sheetcan be recycled back into the oxygen-scavenging layer of the sheet orfilm. It is also possible to recycle the multilayer sheet back into allof the layers of the sheet.

[0074] Packaging walls and packaging articles according to the presentinvention may contain one or more layers which are foamed. Any suitablepolymeric foaming technique, such as bead foaming or extrusion foaming,can be utilized. For example, a packaging article can be obtained inwhich a foamed resinous layer comprising, for example, foamedpolystyrene, foamed polyester, foamed polypropylene, foamed polyethyleneor mixtures thereof, can be adhered to a solid resinous layer containingthe oxygen-scavenging composition of the present invention.Alternatively, the foamed layer may contain the oxygen-scavengingcomposition, or both the foamed and the non-foamed layer can contain thescavenging composition. Thicknesses of such foamed layers normally aredictated more by mechanical property requirements, e.g. rigidity andimpact strength, of the foam layer than by oxygen-scavengingrequirements.

[0075] Packaging constructions such as those described above can benefitfrom the ability to eliminate costly passive barrier films.Nevertheless, if extremely long shelf life or added oxygen protection isrequired or desired, a packaging wall according to the invention can befabricated to include one or more layers of EVOH, nylon or PVDC, or evenof metallized polyolefin, metallized polyester, or aluminum foil.Another type of passive layer which may be enhanced by anoxygen-scavenging resin layer according to the present invention issilica-coated polyester or silica-coated polyolefin. In cases where amultilayer packaging wall according to the invention contains layers ofdifferent polymeric compositions, it may be preferable to use adhesivelayers such as those based on ethylene-vinyl acetate copolymer ormaleated polyethylene or polypropylene, and if desired, the oxygenscavenger of the present invention can be incorporated in such adhesivelayers. It is also possible to prepare the oxygen-scavenging compositionof the present invention using a gas barrier resin such as EVOH, nylonor PVDC polymer in order to obtain a film having both active and passivebarrier properties.

[0076] While the focus of one embodiment of the invention is upon theincorporation of the oxygen-scavenging composition directly into thewall of a container, the oxygen-scavenging compositions also can be usedin packets, as a separate inclusion within a packaging article where theintent is only to absorb headspace oxygen.

[0077] A primary application for the oxygen-scavenging resin, packagingwalls, and packaging articles of the invention is in the packaging ofperishable foods. For example, packaging articles utilizing theinvention can be used to package milk, yogurt, ice cream, cheese; stewsand soups; meat products such as hot dogs, cold cuts, chicken, beefjerky; single-serving pre-cooked meals and side dishes; homemade pastaand spaghetti sauce; condiments such as barbecue sauce, ketchup,mustard, and mayonnaise; beverages such as fruit juice, wine, and beer;dried fruits and vegetables; breakfast cereals; baked goods such asbread, crackers, pastries, cookies, and muffins; snack foods such ascandy, potato chips, cheese-filled snacks; peanut butter or peanutbutter and jelly combinations, jams, and jellies; dried or freshseasonings; and pet and animal foods; etc. The foregoing is not intendedto be limiting with respect to the possible applications of theinvention. Generally speaking, the invention can be used to enhance thebarrier properties in packaging materials intended for any type ofproduct which may degrade in the presence of oxygen.

[0078] Still other applications for the oxygen-scavenging compositionsof this invention include the internal coating of metal cans, especiallyfor oxygen-sensitive food items such as tomato-based materials, babyfood and the like. Typically the oxygen-scavenging composition can becombined with polymeric resins such as thermosets of epoxy, oleoresin,unsaturated polyester resins or phenolic based materials and thematerial applied to the metal can by methods such as roller coating orspray coating.

[0079] The examples provided below are for purposes of illustration andare not intended to limit the scope of invention.

[0080] For purposes of the following examples, oxygen-scavengingperformance was measured according to an Oxygen Absorption Testperformed in a 500 ml glass container containing the oxygen-scavengingcomposition in the form of powder, concentrate pellet or film. Distilledwater or an aqueous salt solution in an open vial was placed inside theglass container next to the samples to be tested in order to control therelative humidity in the container. The container was then sealed andstored at the test temperature. The residual oxygen concentration in theheadspace of the container was measured initially and then periodicallyusing a Servomex Series 1400 Oxygen Analyzer or MOCON Oxygen Analyzer.The amount of oxygen absorbed by the test sample was determined from thechange in the oxygen concentration in the headspace of the glasscontainer. The test container had a headspace volume of about 500 ml andcontained atmospheric air so that about 100 ml of oxygen were availablefor reaction with the iron. Test samples having an iron content of about0.5 gm Fe were tested. For the test system, iron oxidized from metal toFeO has a theoretical oxygen absorption level of 200 cc O₂/gm Fe andiron oxidized from metal to Fe₂O₃ has a theoretical oxygen absorptionlevel of 300 cc O₂/gm Fe. In all of the examples, oxygen scavengercomponent percentages are in weight percents based on total weight ofthe compositions, whether film, powder or pellet, tested for oxygenabsorption.

EXAMPLE 1

[0081] Various powder mixtures of iron powder (SCM Iron Powder A-131);sodium chloride (Morton pulverized salt, Extra Fine 200); bentonite clay(Whittaker, Clarke & Davis, WCD-670); anhydrous sodium acidpyrophosphate (“SAP”), Na₂H₂P₂O₇ (Sigma #7758-16-9); sodiumpyrophosphate decahydrate (“SPH”), Na₄P₂O₇.10H₂O (Aldrich 22,136-8) andanhydrous sodium pyrophosphate (“SPA”), Na₄P₂O₇ (Aldrich 32,246-6) wereprepared as described below. Upon water absorption, SAP has a pH of 4and SPH and SPA each has a pH of 10. The bentonite clay had been driedseparately overnight at 250° C. in a vacuum oven. The desired weights ofingredients were dry blended in a Waring blender and the blendedingredients were stored under a nitrogen atmosphere. Samples 1-1 and 1-2and comparative samples Comp 1-A through Comp 1-I were tested for oxygenabsorption at test conditions of 168 hr, a relative humidity of 100% anda temperature of 22° C. Results are tabulated below. This Exampledemonstrates that the oxygen-scavenging compositions of this inventionemploying iron, sodium chloride and SAP provide equivalent or betteroxygen absorbing efficiency than compositions of iron and sodiumchloride with or without clay. Comparative compositions with iron,sodium chloride and SPH or SPA exhibit considerably lower oxygenabsorption values. Also, comparative compositions with iron and clay,SAP, SPH or SPA all exhibited very low values of oxygen absorption withno electrolyte compound, sodium chloride, present. Powder Additive,Clay, cc O₂ No. Fe, % NaCl, % Additive % % gm Fe 1-1 50 37.5 SAP 12.5 0204 1-2 44.4 33.3 SAP 11.1 11.1 169 Comp 1-A 100 0 — 0 0 5 Comp 1-B 57.142.9 — 0 0 202 Comp 1-C 50 37.5 — 0 12.5 204 Comp 1-D 50 37.5 SPH 12.5 074 Comp 1-E 50 37.5 SPA 12.5 0 44 Comp 1-F 80 0 — 0 20 39 Comp 1-G 80 0SAP 20 0 17 Comp 1-H 80 0 SPH 20 0 2 Comp 1-I 80 0 SPA 20 0 2

EXAMPLE 2

[0082] A dry-mix preparation of oxygen scavenger ingredients was carriedout in the following manner: Iron powder (SCM Iron Powder A-131); sodiumchloride 24(Morton pulverized salt, Extra Fine 200); bentonite clay(Whittaker, Clarke & Davis, WCD-670) and anhydrous sodium acidpyrophosphate (SAP), Na₂H₂P₂O₇ (Sigma #7758-16-9) were dry blended in aWaring blender at a weight ratio of Fe:NaCl:bentonite clay:Na₂H₂P₂O₇ of4:3:1:2. The bentonite clay had been dried separately overnight at 250°C. in a vacuum oven. The blended oxygen scavenger ingredients werestored under nitrogen. A concentrate of oxygen scavenger and polymerresin was prepared from a 50/50 weight ratio of linear low densitypolyethylene granules (GRSN 7047, Union Carbide) and the oxygenscavenger composition by tumble mixing in a bucket/bottle roller for tenminutes to obtain a homogeneous mixture. The resultant powder blend wasfed directly to the hopper of a 19 mm conical corotating twin-screwextruder equipped with a strand die. The zone temperatures of theextruder barrel were set as follows: zone 1—215° C., zone 2—230° C.,zone 3—230° C., and strand die—230° C. The extrudate was cooled withroom-temperature water in a water bath and chopped into pellets with apelletizer. The pellets were dried overnight at 100° C. in a vacuum ovenand stored under nitrogen.

EXAMPLE 3

[0083] Low density polyethylene oxygen-scavenging films were prepared byextruding a mixture containing 80 parts by weight (pbw) low densitypolyethylene pellets (DOW 526 I, Dow Chemical) having a nominal oxygenpermeation coefficient (OPC) of 1.5-2.1×10⁻¹⁰ cc-cm/cm²-sec-cm Hg, asmeasured at a temperature of 20° C. and a relative humidity of 0%, and20 pbw of an oxygen-scavenging composition in the form of a concentrateprepared according to the procedure described in Example 2. Theconcentrates contained various amounts of iron, sodium chloride,bentonite clay and SAP as tabulated below with the weight ratio ofsodium chloride to iron maintained at about 0.75:1. Films were preparedusing a Haake Rheomex 245 single screw extruder (screw diameter-19 mm;UD ratio-25:1). The zone temperatures of the extruder barrel were set asfollows: zone 1—245° C., zone 2—250° C., zone 3—250° C. and die—230° C.Nominal thicknesses of the extruded films were 5 mils. Tabulated belowis the amount of oxygen absorbed by each of the film samples as measuredby the Oxygen Absorption Test described above at test conditions of 168hr, a relative humidity of 100% and a temperature of 22° C. This exampledemonstrates that at a given weight ratio of sodium chloride to iron,addition of SAP significantly increases the oxygen absorption of the lowdensity polyethylene oxygen-scavenging film. Film No. Iron, % NaCl, %SAP, % Clay, % cc O₂ gm Fe 3-1 4.00 3.00 2.00 1.00 92 3-2 4.44 3.33 1.111.11 50 3-3 4.71 3.53 0.59 1.18 51

EXAMPLE 4

[0084] Low density polyethylene oxygen-scavenging films were prepared bythe same procedure as described in Example 3. The low densitypolyethylene films contained various amounts of iron, sodium chloride,bentonite clay and SAP as tabulated below with the weight ratio of SAPto iron held constant at a value of 0.5:1. Tabulated below is the amountof oxygen absorbed by each of the film samples as measured by the OxygenAbsorption Test described above at test conditions of 168 hr, a relativehumidity of 100% and a temperature of 22° C. This example demonstratesthat for low density polyethylene films containing iron, SAP and sodiumchloride at a given weight ratio of SAP to iron, sodium chlorideincreased the oxygen-scavenging capacity of the low density polyethylenefilm and that as the amount of sodium chloride was increased, theoxygen-scavenging capacity of the film also increased. Film No. Iron, %NaCl, % SAP, % Clay, % cc O₂ gm Fe 4-1 5.56 0.28 2.78 1.39 33 4-2 5.330.67 2.67 1.33 56 4-3 5.13 1.03 2.56 1.28 60 4-4 4.00 3.00 2.00 1.00 92

EXAMPLE 5

[0085] Concentrates of the ingredient mixtures of Example 4 and polymerresin were prepared at a 50/50 weight ratio with linear low densitypolyethylene granules (GRSN 7047, Union Carbide) by tumble mixing thecomponents in a bucket/bottle roller for ten minutes to obtain ahomogeneous mixture. The resulting blends were formed into pellets bythe procedure described in Example 2 and the concentrates were mixedwith low density polyethylene pellets (Dow 5261, Dow Chemical) in a 1:4weight ratio and these pellet blends formed into films foroxygen-scavenging testing. The films were tested at conditions of 168hr, a relative humidity of 100% and a temperature of 22° C. The amountof thermoplastic polymer in the film was 90 weight % and thecompositions of the remaining components are tabulated below togetherwith the oxygen absorbed. This example demonstrates that theoxygen-scavenging composition of this invention comprising athermoplastic resin, iron, sodium chloride and SAP provides equivalentor better oxygen absorbing efficiency than the thermoplastic resin, ironand sodium chloride, with or without clay. Comparative compositions witha thermoplastic resin, iron, sodium chloride and SPH or SPA all exhibitconsiderably lower oxygen absorption values. Also, comparativecompositions with no electrolyte compound, sodium chloride, present allexhibited very low values of oxygen absorption. The water of hydrationof the SPH led to processing difficulties during film extrusion. FilmAdditive, Clay, cc O₂ No. Fe, % NaCl, % Additive % % gm Fe 5-1 5.00 3.75SAP 1.25 0 54 5-2 4.44 3.33 SAP 1.11 1.11 40 Comp 5-A 10.0 0 — 0 0 0.3Comp 5-B 5.71 4.29 — 0 0 23 Comp 5-C 5.00 3.75 — 0 1.25 27 Comp 5-D 5.003.75 SPH 1.25 0 4 Comp 5-E 5.00 3.75 SPA 1.25 0 5 Comp 5-F 8.00 0 — 02.00 1 Comp 5-G 8.00 0 SAP 2.00 0 3 Comp 5-H 8.00 0 SPH 2.00 0 0.6 Comp5-I 8.00 0 SPA 2.00 0 0.5

Comparative Example A

[0086] Comparative, extruded low density polyethylene films wereprepared by extruding a mixture containing 80 pbw low densitypolyethylene pellets (DOW 526 l, Dow Chemical) and 20 pbw ofconcentrates prepared according to Example 2 with various amounts ofcitric acid tripotassium salt (“CATP”) as the addative. Citric acidtripotassium salt upon water absorption has a pH of 9. The extrudedfilms were prepared according to the method described in Example 3 withthe films having nominal thicknesses of 5 mils. The amounts of oxygenabsorbed by the film samples as measured by the Oxygen Absorption Testdescribed above at test conditions of 168 hr, a relative humidity of100% and a temperature of 22° C. are given below. This comparativeexample demonstrates that citric acid tripotassium salt, having a pHgreater than 7 upon water absorption, when added to NaCl is ineffectivein enhancing oxygen-scavenging properties. Comparative films B-3 and B-4with only SAP or sodium chloride as the additive exhibited oxygenabsorption values of 3 and 26 cc O₂/gm Fe, respectively. cc O₂ Film No.Iron, % NaCl, % CATP, % SAP, % Clay, % gm Fe B-1 4.44 3.33 1.11 0 1.11 0B-2 4.00 3.00 2.00 0 1.00 1 B-3 5.71 0 0 2.86 1.43 3 B-4 5.00 3.75 0 01.25 26

EXAMPLE 6

[0087] Low density polyethylene films were prepared by extruding amixture containing 80 pbw low density polyethylene pellets (DOW 526 I,Dow Chemical) and 20 pbw of a concentrate prepared according to Example2 with various amounts of nicotinic acid (“NIT”) and sodium chloride.Nicotinic acid upon water absorption has a pH of 4-5. The extruded filmswere prepared according to the method described in Example 3 with thefilms having nominal thicknesses of 5 mils. The amount of oxygenabsorbed by the film samples as measured by the Oxygen Absorption Testdescribed above after 168 hr at a relative humidity of 100% and atemperature of 220° C. is tabulated below. This example demonstratesthat nicotinic acid in combination with sodium chloride can improveoxygen-scavenging ability and that nicotinic acid without theelectrolyte compound, sodium chloride, was not effective in increasingthe oxygen-scavenging ability of the composition. cc O₂ Iron, % NaCl, %Clay, % NIT, % gm Fe 4.00 3.00 1.00 2.00 49 5.71 0 1.43 2.86 4

EXAMPLE 7

[0088] Low density polyethylene oxygen-scavenging films were prepared byextruding a mixture containing 80 pbw low density polyethylene pellets(DOW 526 I, Dow Chemical) having a nominal OPC of 1.5-2.1×10⁻¹⁰cc-cm/cm²-sec-cm Hg, as measured at a temperature of 20° C. and arelative humidity of 0%, and 20 pbw of concentrates containing variousamounts of iron, sodium chloride, bentonite clay and SAP as tabulatedbelow in the manner described according to Example 2. The film wasprepared using a Haake Rheomex 245 single screw extruder (screwdiameter-19 mm; L/D ratio-25:1). The zone temperatures of the extruderbarrel were set as follows: zone 1—245° C., zone 2—250° C., zone 3—250°C. and die—230° C. The extruded films had nominal thicknesses of 5 mils.The amounts of oxygen absorbed by the film samples as measured by theOxygen Absorption Test at test conditions of 168 hr, a relative humidityof 100% and a temperature of 22° C. are given below. This exampledemonstrates good oxygen absorption performance even at low levels ofelectrolyte plus acidifying components but that oxygen absorption waserratic at low electrolyte to acidifier ratios. The latter results arebelieved to have been caused by difficulties in effectively mixing thecompositions with low levels of sodium chloride. cc O₂ Iron, % NaCl, %SAP, % Clay, % gm Fe 5.6 0.3 2.8 1.4 55 6.5 0.3 1.6 1.6 69 7.1 0.4 0.71.8 50 7.4 0.4 0.4 1.9 44 7.6 0.4 0.2 1.9 49 5.7 0.06 2.8 1.4 45 6.60.07 1.7 1.7 19 7.4 0.07 0.7 1.8 29 7.6 0.08 0.4 1.9 15 7.8 0.08 0.2 2.046

EXAMPLE 8

[0089] Low density polyethylene oxygen-scavenging films were prepared byextruding a mixture containing 80 pbw low density polyethylene pellets(DOW 526 I, Dow Chemical) having a nominal OPC of 1.5-2.1×10⁻¹⁰cc-cm/cm²-sec-cm Hg, as measured at a temperature of 20° C. and arelative humidity of 0%, and 20 pbw of concentrates prepared accordingto Example 2 with iron, bentonite clay, citric acid and sodium chloride.Upon water absorption, citric acid has a pH of 1-2. The films wereprepared according to the method described in Example 3 with theextruded films having nominal thicknesses of 5 mils. The amounts ofoxygen absorbed by the film samples as measured by the Oxygen AbsorptionTest described above at test conditions of 168 hr, a relative humidityof 100% and a temperature of 22° C. are given below. This exampledemonstrates that with an acidifier compound of high acidity, the amountof oxygen absorbed was significantly increased. Citric Acid, AdditiveIron, % NaCl, % % Clay, % cc O₂ gm Fe 0 5.00 3.75 0 1.25 26 Citric Acid4.44 3.33 1.11 1.11 174 Citric Acid 4.00 3.00 2.00 1.00 197

EXAMPLE 9

[0090] Two separate concentrate preparations of various oxygen scavengeringredients were carried out in the following manner: In oneconcentrate, iron powder (SCM iron Powder A-131); sodium chloride(Morton pulverized salt, Extra Fine 325); and bentonite clay (Whittaker,Clarke & Davis, WCD-670) were mixed in a high intensity Henschel mixerin a weight ratio of Fe:NaCl:bentonite clay of 4:3:1. The mixedingredients were fed at a 50:50 by weight ratio with linear low densitypolyethylene powder (Dowlex 2032, Dow Chemical) to a Werner & PfleidererZSK-40 twin-screw extruder to form concentrate pellets. A secondconcentrate of 25 weight percent of anhydrous sodium acid pyrophosphate,(Sigma #7758-16-9) with linear low density polyethylene powder was alsoprepared in a ZSK-40 twin-screw extruder. Films of polyethyleneterephthalate (“PET”) (nominal OPC of 1.8-2.4×10⁻¹² cc-cm/cm²-sec-cmHg), polypropylene (“PP”) (nominal OPC of 0.9-1.5×10⁻¹⁰ cc-cm/cm²-sec-cmHg), low density polyethylene (“LDPE”) and linear low densitypolyethylene (“LLDPE”) with various combinations of the aboveconcentrates were extruded. In all of the films, the weight ratio ofsodium chloride to iron was held constant at 0.75:1. The amounts ofoxygen absorbed by these film samples as measured by the OxygenAbsorption Test at test conditions of 168 hr, a temperature of 22° C.and a relative humidity of 100% are tabulated below. Resin Fe, % NaCl, %SAP, % Clay, % cc O₂ gm Fe PET 5.00 3.75 0 1.25 10 PET 4.00 3.00 1.001.00 14 PET 4.00 3.00 2.00 1.00 14 PP 5.00 3.75 0 1.25 28 PP 4.00 3.001.00 1.00 46 PP 4.00 3.00 2.00 1.00 50 LLDPE 5.00 3.75 0 1.25 39 LLDPE4.00 3.00 1.00 1.00 99 LLDPE 4.00 3.00 2.00 1.00 98 LDPE 5.00 3.75 01.25 29 LDPE 4.00 3.00 1.00 1.00 41 LDPE 4.00 3.00 2.00 1.00 48

EXAMPLE 10

[0091] Two separate concentrates were prepared by the same procedure asin Example 9. One concentrate consisted of iron powder (SCM iron powderA-131); sodium chloride (Morton pulverized salt, Extra Fine 325);bentonite clay (Whittaker, Clarke & Davis, WCD-670); and linear lowdensity polyethylene resin (Dowlex 2032, Dow Chemical) in a weight ratioof Fe:NaCl:bentonite clay:LLDPE of 4:3:1:8. The second concentrateconsisted of sodium acid pyrophosphate (Sigman #7758-16-9) and linearlow density polyethylene (Dowlex 2032, Dow Chemical) in a weight ratioof SAP:LLDPE of 1:3. Low density polyethylene oxygen-scavenging filmswere prepared by the same procedure as described in Example 3 using aHaake Rheomex 245 single screw extruder. The film processingtemperatures varied from nominal 243° C. to nominal 260° C. to nominal288° C. At nominal 243° C., the zone temperatures of the extruder barrelwere set as follows: zone 1—241° C., zone 2—243° C., zone 3—243° C. anddie—218° C. At nominal 260° C., the zone temperatures of the extruderbarrel were set as follows: zone 1—254° C., zone 2—260° C., zone 3—260°C. and die—232° C. At nominal 288° C., the zone temperatures of theextruder barrel were set as follows: zone 1—282° C., zone 2—285° C.,zone 3—288° C. and die—252° C. At the higher processing temperatures,the resulting films were found to contain voids believed to have beencaused by decomposition of sodium acid pyrophosphate. Thermalgravimetric analysis of sodium acid pyrophosphate powder heated fromroom temperature to about 610° C. at a rate of about 10° C./minuteindicated weight loss occurring from about 260 to 399° C., correspondingto loss of water from sodium acid pyrophosphate, thus suggestingdecomposition thereof to NaPO₃. Based on these observations, it isbelieved that the higher processing temperatures used in this exampleled to decomposition of the sodium acid pyrophosphate that wasoriginally used to sodium metaphosphate, sodium trimetaphosphate, sodiumhexameta-phosphate, each having a pH in the range of 4-6 in aqueoussolution, or a combination thereof. The amounts of oxygen absorbed bythese film samples as measured by the Oxygen Absorption Test at testconditions of 168 hr, a temperature of 22° C. and a relative humidity of100% are tabulated below. Nominal Film Film Processing cc O₂ No. Temp, °C. Iron, % NaCl, % SAP, % Clay, % gm Fe 10-1 243 4.44 3.33 1.11 1.11 4010-2 288 4.44 3.33 1.11 1.11 53 10-3 260 11.11 8.33 2.78 2.78 48 10-4288 11.11 8.33 2.78 2.78 77

EXAMPLE 11

[0092] A dry-mix preparation of oxygen scavenger ingredients was carriedout in the following manner: Iron powder (SCM A-131); sodium chloride(Morton EF325); and sodium acid pyrophosphate (Monsanto SAP-28) weremixed at 2/2/1 weight ratio of Fe/NaCl/SAP in an intensive mixingHenschel mixer. The mixing time was about 80 seconds. The powder mixturewas compounded into nineteen separate resins as shown in the Table belowat a 1/1 weight ratio on a twin-screw ZSK-30 extruder. The zonetemperatures of the extruder barrel were set as follows: zone 1—140-200°C., zone 2—220-280° C., zone 3—230-270° C., zone 4—220 -260° C. zone5—220-260° C., zone 7—200-250° C. The melt temperature of the extrudatewas in the range of 180-280° C. The extrudate was cooled and choppedinto concentrate pellets of oxygen scavenger resin designatedConcentrates I-XV and Concentrates A-D. The resulting concentrates weremeasured for oxygen-scavenging performance according to the OxygenAbsorption Test described above at 72 hr (3 day), 168 hr (7 days), and672 hr (28 days). The results are tabulated below in Table I and the 1%Secant Modulus and Shore D Hardness are shown in Table II. This Exampledemonstrates that the oxygen-scavenging compositions of this inventionemploying iron, sodium chloride and SAP in a soft, flexible resinprovide better oxygen absorbing efficiency than identical compositionsin more rigid polyethylenes and polypropylenes such as in concentratesA-D TABLE I Oxygen Absorption Performance of Oxygen-ScavengingConcentrate Pellets in Various Carrier Resins Concentrate ResinComposition: 20 wt % Iron 20 wt % Salt 10 wt % SAP 50 wt % Carrier ResinOxygen Scavenger Concentrate Oxygen Absorption (cc O₂/gm Fe) Conc @ 22°C., 100% RH No. Carrier Resin days 7 days 28 days Type/ comonomer I DowAffinity mPE/octene 38, 43 55, 59 91, 95 PF1140 II Dow/DuPont mPE/octene39, 41 55, 58 90, 96 Engage 8440 III Exxon Exact 3131 mPE/hexene 35 5286 IV Exxon Exact 4053 mPE/butene 37 53 79 V Exxon Exact 4151 mPE/hexene53 71 109 VI Amoco EHPP mPP/none 31 45 76 Type/ Styrene:Rubber VII ShellKraton D2103 SBS/35:65 135 166 185 VIII Shell Kraton D2104 SBS/30:70 88125 160 IX Shell Kraton D2109 SBS/22:78 55 85 121 X Shell Kraton G2701SEBS/37:63 37 61 105 XI Shell Kraton G2705 SEBS/30:70 42 65 108 XIIShell Kraton G2706 SEBS/21:79 81 105 138 XIII SIBS SIBS/30:70 58 79 97Type/ comonomer XIV Carbide ULDPE Unipol/higher 69 103 137 ETS9064olefin XV Dow VLDPE Attane LP Solution/ 42 58 88 4202 higher olefin ADow Dowlex Ziegler-Natta/ 25 35 61 LLDPE2032 higher olefin B AmocoPP7200p Ziegler-Natta/ 13 21 39 none C Dow LDPE 6401 Radical/none 20 3160 D Westlake LDPE Radical/none 20 32 55 EF412

[0093] TABLE II Shore Hardness and Secant Modulus Properties of CarrierResins for Oxygen-Scavenging Composition Conc Shore 1% Secant No.Carrier Resin D Modulus Type/comonomer I Dow Affinity PF1140 mPE/octene35.6 5,155 II Dow/DuPont Engage mPE/octene 37.2 6,600 8440 III ExxonExact 3131 mPE/hexene 40.6 8,448 IV Exxon Exact 4053 mPE/butene 29.92,866 V Exxon Exact 4151 mPE/hexene 37.7 6,563 VI Amoco EHPP mPP/none19.5 1,837 Type/Styrene: Rubber VII Shell Kraton D2103 SBS/35:65 19.01,386 VIII Shell Kraton D2104 SBS/30:70 8.1 829 IX Shell Kraton D2109SBS/22:78 10.3 454 X Shell Kraton G2701 SEBS/37:63 12.8 1,706 XI ShellKraton G2705 SEBS/30:70 9.1 1,126 XII Shell Kraton G2706 SEBS/21:79 5.9188 XIII SIBS SIBS/30:70 10.9 337 Type/Comonomer XIV Carbide ULDPEUnipol/higher olefin 42.0 20,000 ETS9064 XV Dow VLDPE Attane LPSolution/higher 42.1 18,900 4202 olefin A Dow DowlexZiegler-Natta/higher 47.5 37,115 LLDPE2032 olefin B Amoco PP7200pZiegler-Natta/none 72.4 176,000 C Dow LDPE 6401 Radical/none 46.1 26,526D Westlake LDPE Radical/none 46.2 26,385 EF412

[0094] The oxygen absorption results of Example 11 demonstrate thatoxygen-scavenging compositions in soft, flexible resins absorb moreoxygen per gram of iron than more rigid, hard resins such as LDPE, LLDPEand PP. Although there is not a linear relationship between the softnessand flexibility of a resin and oxygen-absorption, there is ademonstrated improvement between soft, flexible resins on the whole andhard, rigid resins. All of the resins with a Shore D below 45 and 1%secant modulus below about 25,000 p.s.i. absorbed more oxygen per gramof iron than those resins with a Shore D greater than 45 and 1% secantmodulus greater than 25,000 p.s.i. It is believed that the flexiblemolecular structure of soft resins facilitates the intimate contact ofthe oxygen-scavenging components. This enables the electrolyte andacidifying component to promote the oxidation of the iron in the resin.

[0095] As shown in Table I, the styrene-butadiene-styrene blockcopolymers of the Kraton® D series work particularly well. This improvedoxygen absorption may be in part due to the absorption of oxygen by thecarbon-carbon double bonds in the butadiene segments of thestyrene-butadiene block-copolymer.

EXAMPLE 12

[0096] Low density polyethylene oxygen-scavenging films were prepared byblending each of the nineteen concentrates of Example 11, having thesame Shore D and 1% secant Modulus properties listed above, with DowLDPE 640i resin at a 1/1 ratio, and preparing extruded films using asingle Haake extruder. The zone temperatures of the extruder barrel wereset as follows: zone 1—190° C., zone 2—200° C., zone 3—210° C. and diezone—200° C. The extruded films had a nominal thickness of 5 mils. Theresulting films, designated Film I-XV and Comparative Film A-D, weremeasured for oxygen-scavenging performance according to the OxygenAbsorption Test described above at 72 hr (3 day), 168 hr (7 days), and672 hr (28 days). The results are tabulated below. This Exampledemonstrates that the oxygen-scavenging LDPE films of this inventionemploying iron, sodium chloride and SAP in a soft, flexible carrierresin concentrate blended with the LDPE resin provide better oxygenabsorbing efficiency than identical compositions in more rigidpolyethylene and polypropylene concentrates A-D blended with LDPE filmresin. TABLE III Oxygen Absorption Performance of Extrusion FilmsContaining Oxygen-Scavenging Compositions in Various Carrier ResinsExtrusion Film Composition: 50 wt % Concentrate Resin from Table I 50 wt% LDPE Film Resin Oxygen Scavenger Concentrate Oxygen Absorption (ccO₂/gm Fe) Conc @ 22° C., 100% RH No. Carrier Resin days 7 days 28 daysType/ comonomer I Dow Affinity mPE/octene 77 96 126 PF1140 II Dow/DuPontmPE/octene 54 64 84 Engage 8440 III Exxon Exact 3131 mPE/hexene 82 100127 IV Exxon Exact 4053 mPE/butene 64 73 92 V Exxon Exact 4151mPE/hexene 75 88 116 VI Amoco EHPP mPP/none 73 85 94 Type/Styrene:Rubber VII Shell Kraton D2103 SBS/35:65 110 128 143 VIII ShellKraton D2104 SBS/30:70 85 95 111 IX Shell Kraton D2109 SBS/22:78 104 156187 X Shell Kraton G2701 SEBS/37:63 47 64 81 XI Shell Kraton G2705SEBS/30:70 47 62 79 XII Shell Kraton G2706 SEBS/21:79 63 69 84 XIII SIBSSIBS/30:70 80 107 122 Type/ comonomer XIV Carbide ULDPE Unipol/higher 5768 87 ETS9064 olefin XV Dow VLDPE Attane LP Solution/ 66 88 119 4202higher olefin A Dow Dowlex Ziegler-Natta/ 36 40 61 LLDPE2032 higherolefin B Amoco PP7200p Ziegler-Natta/ 18 28 43 none C Dow LDPE 6401Radical/none 44 57 79 D Westlake LDPE Radical/none 44 51 65 EF412

[0097] The oxygen absorption results of Example 12 demonstrate thatoxygen-scavenging compositions in soft, flexible resin concentrates thatare further blended with LDPE to form LDPE films, absorb more oxygen pergram of iron than those same compositions in more rigid, hardconcentrate resins further blended with LDPE to form LDPE films.Comparison of the results from Example 11 to Example 12, shows that someresins absorbed oxygen more effectively in concentrate form. But,overall, the soft, flexible carrier resins performed better than thehard, rigid carrier resins in concentrates and films. It is believedthat the difference between concentrate vs. film absorption results maybe due to the compatibility of the concentrate carrier and film resin.We believe that if the concentrate carrier resin is miscible in the filmresin when blended with the film resin, the regions of soft, flexibleresin containing the oxygen-scavenging composition may not exist. Ifthose regions do not exist, the hard, stiff film resin may effect theoxygen absorption ability of the oxygen-scavenging composition in thesame manner the hard, stiff resins lower absorption in the resinconcentrate form. For example, the Kraton G series absorbs more oxygenper gram of iron in the concentrate form versus the LDPE film. This maybe due to the fact that styrene-ethylene-butylene styrene blockcopolymers are readily miscible in LDPE. This miscibility may cause thebreak down of the soft, flexible resin regions, leaving theoxygen-scavenging components in the more rigid LDPE resin.

EXAMPLE 13

[0098] In accordance with Example 11, a dry-mix preparation of oxygenscavenger ingredients was carried out in the following manner: Ironpowder (SCM A-131); sodium chloride (Morton EF325); and sodium acidpyrophosphate (Monsanto SAP-28) were mixed at 2/2/1 ratio of Fe/NaCl/SAPin an intensive mixing Henschel mixer. The powder mixture was compoundedinto two separate resins (Dow/DuPont Engage 8440 and Dow AffinityPF1140) at a 1/1 weight ratio on a twin-screw ZSK-30 extruder to makeconcentrate pellets of oxygen scavenger resin designated ConcentratesC-1 and C-2. Polypropylene oxygen-scavenging films were prepared byblending each of the concentrates with Amoco PP6219 polypropylene resinat a 1/1 ratio, and preparing 5 ml extrusion films using a single screwHaake extruder in accordance with Example 12. The resulting films,designated F-1 and F-2, were measured for oxygen-scavenging performanceaccording to the Oxygen Absorption Test described above at 72 hr (3day), 168 hr (7 days), and 672 hr (28 days). The results are tabulatedbelow. This Example demonstrates that mPE is as effective as a carrierresin in polypropylene as a diluent as it is when LDPE is the diluent.

[0099] Concentrate Resin Composition:

[0100] 20 wt % Iron

[0101] 20 wt % Salt

[0102] 0 Wt % Clay

[0103] 10 wt % SAP

[0104] 50 wt % Carrier Resin Conc. No. Carrier Resin Type/comonomer C-1Dow/DuPont Engage 8440 mPE/octene C-2 Dow Affinity PP1140 mPE/octene

[0105] Extrusion Film Composition

[0106] 50 wt % Concentrate Resin C1-C2

[0107] 50 wt % Amoco PP6219 Film Resin Oxygen Scavenger Extrusion FilmOxygen Absorption (cc O₂/gm Fe) Film @ 22° C., 100% RH No. Concentrate 3days 7 days 28 days F-1 C-1 56 77 108 F-2 C-2 59 96 110

[0108] The following Examples 14-16 demonstrate the effect of dehydratedacidifying components on the appearance and oxygen-absorption of theoxygen-scavenging films. In each of the Examples below, a high extrusiontemperature—above 270° C.—was used to approximate the high temperatureextrusion coating process temperature.

EXAMPLE 14

[0109] Calcination of SAP

[0110] Commercial food-grade sodium acid pyrophosphate (Na₂H₂P₂O₇,Monsanto SAP-28) was calcined at 350° C. for 2 hours in a microwavefurnace to give a dehydrated product. The weight loss during calcinationwas 8.1 wt %. The pH of a 0.1 wt % aqueous slurry/solution of dehydratedSAP was 5.6. The dehydrated SAP was ground and sifted into a finepowder, and then mixed with iron powder (SCM A-131), salt powder (MortonEF325) at 2/2/1 weight ratio of iron/salt/dehydrated SAP in an intensivemixing Waring mixer. The powder mixture was further mixed with ExxonLLDPE resin powder (Escorene LL-5002.09) at 1/3 ratio of inorganic/resinin the mixer.

[0111] The mixture of oxygen scavenger components and resin wascompounded into an oxygen scavenger resin composition, and further madeinto extruded film on a Haake extruder at 310° C. The extrudertemperature profile was 280, 295, 310, and 265 ° C. at Zone 1, 2, 3 and4 (die). The polymer melt temperature was 310° C. The extruded film(designated Film I) showed clean and smooth appearance with no voids orbubbles in the film. The oxygen absorption performance of the filmsample was measured and found to be good, as shown in Table IV.

[0112] For comparison, commercial food-grade sodium acid pyrophosphate(Na₂H₂P₂O₇, Monsanto SAP-28) was used without calcination. The pH of the0.1 wt % aqueous slurry/solution of SAP was 4.2. It was mixed with ironpowder (SCM A-131), salt powder (Morton EF325) at 2/2/1 weight ratio ofiron/saltSAP in an intensive mixing Waring mixer. The powder mixture wasfurther mixed with Exxon LLDPE resin powder (Escorene LL-5002.09) at 1/3ratio of inorganic/resin in the mixer.

[0113] The mixture of oxygen scavenger components and resin wascompounded into an oxygen scavenger resin, and further made intoextruded film on a Haake extruder at 310° C. The extruder temperatureprofile was 280, 295, 310, and 265° C. at Zone 1, 2, 3 and 4 (die). Thepolymer melt temperature was 310° C. The extruded film (designated FilmA) showed poor appearance with many large voids and bubbles in the film.The oxygen absorption performance of the film sample was measured andfound to be very good, as shown in Table IV.

EXAMPLE 15

[0114] Calcination of MCP

[0115] Commercial food-grade monocalcium phosphate monohydrate(CaH₄(PO₄)₂.H₂O, Rhone-Poulenc Regent 12xx) was calcined at 350 ° C. for2 hours in a microwave furnace to give a dehydrated product. The weightloss during calcination was 18.6 wt %. The pH of the 0.1 wt % aqueousslurry/solution of dehydrated MCP was 3.0.

[0116] It was ground and sifted into a fine powder, and then mixed withiron powder (SCM A-131), salt powder (Morton EF325) at 2/2/1 weightratio of iron/salt/dehydrated MCP in an intensive mixing Waring mixer.The powder mixture was further mixed with Exxon LLDPE resin powder(Escorene LL-5002.09) at 1/3 ratio of inorganic/resin in the mixer.

[0117] The mixture of oxygen scavenger components and resin wascompounded into an oxygen scavenger resin, and further made intoextruded film on a Haake extruder at 310° C. The extruder temperatureprofile was 280, 295, 310, and 265° C. at Zone 1, 2, 3 and 4 (die). Thepolymer melt temperature was 310° C. The extruded film (designated FilmII) showed clean and smooth appearance with no voids or bubbles in thefilm. The oxygen absorption performance of the film sample was measuredand found to be good, as shown in Table IV.

[0118] For comparison, commercial food-grade monocalcium phosphatemonohydrate (CaH₄(PO₄)₂.H₂O, Rhone-Poulenc Regent 12xx) was used withoutcalcination. The pH of the 0.1 wt % aqueous (slurry) solution of MCP was4.0. It was mixed with iron powder (SCM A-131), salt powder (MortonEF325) at 2/2/1 weight ratio of iron/salt/MCP in an intensive mixingWaring mixer. The powder mixture was further mixed with Exxon LLDPEresin powder (Escorene LL-5002.09) at 1/3 ratio of inorganic/resin inthe mixer.

[0119] The mixture of oxygen scavenger components and resin wascompounded into an oxygen scavenger resin, and further made intoextruded film on a Haake extruder at 310° C. The extruder temperatureprofile was 280, 295, 310, and 265° C. at Zone 1, 2, 3 and 4 (die). Thepolymer melt temperature was 310° C. The extruded film (designated FilmB) showed poor appearance with many large voids and bubbles in the film.The oxygen absorption performance of the film sample was measured andfound to be very good, as shown in Table IV.

EXAMPLE 16

[0120] Calcination of STMP

[0121] Commercial food-grade sodium trimetaphosphate ((NaPO₃)₃, MonsantoSTMP) was calcined at 350° C. for 1 hour in a microwave furnace to givea dehydrated product. The weight loss during calcination was 0.5 wt %.The pH of the 0.1 wt % aqueous slurry/solution of dehydrated STMP was5.4. It was ground and sifted into a fine powder, and then mixed withiron powder (SCM A-131), salt powder (Morton EF325) at 2/2/1 weightratio of iron/salt/dehydrated STMP in an intensive mixing Waring mixer.The powder mixture was further mixed with Exxon LLDPE resin powder(Escorene LL-5002.09) at 1/3 ratio of inorganic/resin in the mixer.

[0122] The mixture of oxygen scavenger and resin was compounded into anoxygen scavenger resin, and further made into extruded film on a Haakeextruder at 310° C. The extruder temperature profile was 280, 295, 310,and 265° C at Zone 1, 2, 3 and 4 (die). The polymer melt temperature was310° C. The extruded film (designated Film III) showed clean and smoothappearance with no voids or bubbles in the film. The oxygen absorptionperformance of the film sample was measured and found to be good, asshown in Table IV.

[0123] For comparison, commercial food-grade sodium trimetaphosphate((NaPO₃)₃, Monsanto STMP) was used without calcination. The pH of the0.1 wt % aqueous (slurry) solution of STMP was 5.2. It was mixed withiron powder (SCM A-131), salt powder (Morton EF325) at 2/2/1 weightratio of iron/salt/STMP in an intensive mixing Waring mixer. The powdermixture was further mixed with Exxon LLDPE resin powder (EscoreneLL-5002.09) at 1/3 ratio inorganic/resin in the mixer.

[0124] The mixture of oxygen scavenger and resin was compounded into anoxygen scavenger resin, and further made into extruded film on a Haakeextruder at 310° C. The extruder temperature profile was 280, 295, 310,and 265° C. at Zone 1, 2, 3 and 4 (die). The polymer melt temperaturewas 310° C. The extruded film (designated Film C) showed somewhat poorappearance with minor/small voids and bubbles in the film. The oxygenabsorption performance of the film sample was measured and found to begood, as shown in Table IV.

Counter Example D

[0125] No Acidifying Component

[0126] Iron powder (SCM A-131) and salt powder (Morton EF325) were mixedat 1/1 ratio in an intensive mixing Waring mixer. No acidifyingcomponent was used in the formulation. The powder mixture was furthermixed with Exxon LLDPE resin powder (Escorene LL-5002.09) at 1/3 ratioof inorganic/resin in the mixer.

[0127] The mixture of oxygen scavenger and resin was compounded into anoxygen scavenger resin, and further made into extruded film on a Haakeextruder at 310° C. The extruder temperature profile was 280, 295, 310,and 265° C. at Zone 1, 2, 3 and 4 (die). The polymer melt temperaturewas 310° C. The extruded film (designated Film D) showed clean andsmooth appearance with no voids or bubbles in the film. The oxygenabsorption performance of the film sample was measured and found to bepoor, as shown in Table IV. TABLE IV Oxygen Absorption Performance ofOxygen-Scavenging Films Oxygen Absorption (cc O2/gm Fe) after Sample 6days, @ 22° C., ID pH Modifier Film Appearance 100% RH Film I CalcinedSAP Good, no voids 44.0 Film II Calcined MCP Good, no voids 65.5 FilmIII Calcined STMP Good, no voids 38.5 Film A SAP Poor, many large voids165 Film B MCP Poor, many large voids 158 Film C STMP Somewhat poor,minor 53.0 voids Film D No acidifying Good, no voids 12.2 component

[0128] The oxygen-absorption results of Table IV demonstrate twoimportant points. First, that use of an acidifying component improvesthe oxygen absorption of the iron regardless of whether the acidifyingcomponent contains hydrate or is dehydrated. Second, that there is atrade-off between oxygen absorption and film appearance when usinghydrated versus dehydrated acidifying components. If the fabricationtemperature of the film or article is below the dehydration temperatureof the hydrated acidifying component, then the hydrated acidifyingcomponent may be used without the creation of voids or bubbles. If,however, the fabrication temperature is above the dehydrationtemperature of the hydrated acidifying component, a calcined acidifyingcomponent should be used. Although the oxygen absorption decreases whencalcined acidifying components are used, the film appearance is smoothwith no voids or bubbles. The selection of acidifying component willdepend on the end-use application, but an acidifying component—hydratedor calcined—should always be used to achieve increased oxygenabsorption.

We claim:
 1. An oxygen-scavenging composition comprising an oxidizable metal component, an electrolyte component, and a non-electrolytic acidifying component that is thermally stable at thermoplastic resin melt fabrication temperatures.
 2. The oxygen-scavenging composition of claim 1 wherein the non-electrolytic acidifying component is thermally stable above 200° C.
 3. The oxygen-scavenging composition of claim 2 wherein the non-electrolytic acidifying component is selected from the group consisting of monocalcium phosphate, potassium acid pyrophosphate, magnesium sulfate, sodium metaphosphate, sodium trimetaphosphate, sodium hexametaphosphate, aluminum sulfate, aluminum potassium sulfate and combinations thereof.
 4. The oxygen-scavenging composition of claim I wherein the non-electrolytic acidifying component is thermally stable above 270° C.
 5. The oxygen-scavenging composition of claim 4 wherein the non-electrolytic acidifying component is selected from the group consisting of calcined products of: monocalcium phosphate, sodium acid pyrophosphate, sodium metaphosphate, sodium trimetaphosphate, sodium phosphate monobasic, sodium hexametaphosphate, potassium phosphate monobasic, potassium acid pyrophosphate and combinations thereof.
 6. The oxygen-scavenging composition of claim 4 wherein the non-electrolytic acidifying component consists of calcined sodium acid pyrophosphate, calcined monocalcium phosphate and combinations thereof.
 7. The oxygen-scavenging composition of claim I comprising about 10 to about 200 parts by weight electrolyte component and non-electrolytic acidifying component per 100 parts by weight oxidizable metal.
 8. An oxygen-scavenging composition comprising an oxidizable metal component, an electrolyte component, a non-electrolytic acidifying component and a polymeric resin with a 1% secant modulus less than about 25,000 p.s.i. and/or a Shore D Hardness less than about
 45. 9. The oxygen-scavenging composition of claim 8 wherein the polymeric resin is selected from the group consisting of: metallocene polyethylenes, styrene-rubber block copolymers, very low density polyethylenes, ultra low density polyethylenes, and elastomeric homopolypropylene.
 10. The oxygen-scavenging composition of claim 9 wherein the polymeric resin is metallocene polyethylene.
 11. The oxygen-scavenging composition of claim 9 wherein the polymeric resin is a styrene-rubber block copolymer.
 12. The oxygen-scavenging composition of claim 11 wherein the styrene-rubber block copolymer is selected from the group consisting of styrene ethylene-butylene block copolymer, styrene butadiene block copolymer, and styrene isobutylene block copolymer.
 13. The oxygen-scavenging composition of claim 8 comprising about 5 to about 150 parts by weight of the oxidizable metal plus electrolyte plus acidifying components per hundred parts by weight of the polymeric resin.
 14. The oxygen-scavenging composition of claim 8 wherein the acidifying component is selected from the group consisting of sodium acid pyrophosphate, monocalcium phosphate, calcined sodium acid pyrophosphate and calcined monocalcium phosphate.
 15. The oxygen-scavenging composition of claim 8 in the form of a fabricated article.
 16. The oxygen-scavenging composition of claim 8 in the form of a concentrate.
 17. The oxygen-scavenging composition of claim 16 further blended with a second polymeric resin in the form of a fabricated article.
 18. The oxygen-scavenging composition of claim 16 further comprising at least one polymeric resin having a 1% secant modulus and Shore D Hardness greater than or equal to the concentrate resin.
 19. An oxygen-scavenging composition comprising iron, sodium chloride, and a non-electrolytic acidifying component selected from the group consisting of: sodium acid pyrophosphate, monocalcium phosphate, calcined sodium acid pyrophosphate or calcined monocalcium phosphate or mixtures thereof; in a polymeric resin with a 1% secant modulus less than about 25,000 p.s.i. and/or a Shore D Hardness less than about 45, wherein the weight ratio of sodium chloride to the non-electrolytic acidifying component is about 10/90 to about 90/10 and about 50 to about 200 parts by weight sodium chloride and non-electrolytic acidifying component are present per hundred parts by weight iron.
 20. An oxygen-scavenging composition comprising an oxidizable metal component, an electrolyte component, a non-electrolytic acidifying component in a polymeric resin with a 1% secant modulus less than about 20,000 p.s.i. and/or a Shore D Hardness less than about
 42. 